Expanding Selection Criteria in Deceased Donor Liver Transplantation for Hepatocellular Carcinoma: Long-term Follow-up of a National Registry and 2 Transplant Centers.

BACKGROUND: This study compares selection criteria for liver transplant (LT) for hepatocellular carcinoma (HCC) for inclusivity and predictive ability to identify the most permissive criteria that maintain patient outcomes. METHODS: The Scientific Registry of Transplant Recipients (SRTR) database was queried for deceased donor LT's for HCC (2003-2020) with 3-y follow-up; these data were compared with a 2-center experience. Milan, University of California, San Francisco (UCSF), 5-5-500, Up-to-seven (U7), HALT-HCC, and Metroticket 2.0 scores were calculated. RESULTS: Nationally, 26 409 patients were included, and 547 at the 2 institutions. Median SRTR-follow-up was 6.8 y (interquartile range 3.9-10.1). Three criteria allowed the expansion of candidacy versus Milan: UCSF (7.7%, n = 1898), Metroticket 2.0 (4.2%, n = 1037), and U7 (3.5%, n = 828). The absolute difference in 3-y overall survival (OS) between scores was 1.5%. HALT-HCC (area under the curve [AUC] = 0.559, 0.551-0.567) best predicted 3-y OS although AUC was notably similar between criteria (0.506 < AUC < 0.527, Mila n = 0.513, UCSF = 0.506, 5-5-500 = 0.522, U7 = 0.511, HALT-HCC = 0.559, and Metroticket 2.0 = 0.520), as was Harrall's c-statistic (0.507 < c-statistic < 0.532). All scores predicted survival to P < 0.001 on competing risk analysis. Median follow-up in our enterprise was 9.8 y (interquartile range 7.1-13.3). U7 (13.0%, n = 58), UCSF (11.1%, n = 50), HALT-HCC (6.4%, n = 29), and Metroticket 2.0 (6.3%, n = 28) allowed candidate expansion. HALT-HCC (AUC = 0.768, 0.713-0.823) and Metroticket 2.0 (AUC = 0.739, 0.677-0.801) were the most predictive of recurrence. All scores predicted recurrence and survival to P < 0.001 using competing risk analysis. CONCLUSIONS: Less restrictive criteria such as Metroticket 2.0, UCSF, or U7 allow broader application of transplants for HCC without sacrificing outcomes. Thus, the criteria for Model for End-stage Liver Disease-exception points for HCC should be expanded to allow more patients to receive life-saving transplantation.

The Impact of Normothermic Machine Perfusion and Acuity Circles on Waitlist Time, Mortality and Cost in Liver Transplantation: A Multi-Center Experience.

BACKGROUND: Ex-situ normothermic machine perfusion (NMP) helps increase the use of extended criteria donor livers. However, the impact of an NMP program on waitlist times and mortality has not been evaluated. METHODS: Adult patients listed for liver transplant (LT) at two academic centers 1/1/2015-9/1/2023 were included (n=2773) to allow all patients >6-months follow-up from listing. Routine NMP was implemented on 10/14/2022. Waitlist outcomes were compared from pre-NMP pre-acuity-circles (n=1,460), pre-NMP with acuity circles (n=842) and with NMP (n=381). RESULTS: Median waitlist time was 79days (IQR 20-232 d) at baseline, 49days (7-182) with acuity circles, and 14days (5-56) with NMP (p<0.001). The rate of transplant-per-100-person-years improved from 61-per-100-person-years to 99-per-100-person-years with acuity circles, and 194-per-100-person-years with NMP (p<0.001). Crude mortality without transplant decreased from 18.3% (n=268/1460), to 13.3% (n=112/843), to 6.3% (n=24/381) p<0.001) with NMP. Incidence of mortality without LT was 15-per-100-person-years before acuity circles, 19-per-100 with acuity circles, and 9-per-100-person-years after NMP (p<0.001). Median MELD at LT was lowest with NMP, but MELD at listing was highest in this era (p<0.0001). Median DRI of transplanted livers at baseline was 1.54 (1.27-1.82), 1.66 (1.42-2.16) with acuity circles, and 2.06 (1.63-2.46) with NMP (p<0.001). Six-month post-LT survival was not different between eras (p=0.322). The total cost of healthcare while waitlisted was lowest in the NMP era ($53,683 vs. $32,687 vs. $23,688, p<0.001); cost-per-day did not differ between eras (p=0.152). CONCLUSION: Implementation of a routine NMP program was associated with reduced waitlist time and mortality without compromising short-term survival after liver transplant despite increased use of riskier grafts. Routine NMP use enables better waitlist management with reduced healthcare costs.

Intensive locoregional therapy before Liver Transplantation for colorectal cancer liver metastasis: A novel pre-transplant protocol.

BACKGROUND: We describe a novel pre-liver-transplant (LT) approach in colorectal liver metastasis (CRLM) allowing for improved monitoring of tumor biology and reduction of disease burden before committing a patient to transplantation. METHODS: Patients undergoing LT for CRLM at Cleveland Clinic were included. The described protocol involves intensive locoregional therapy with systemic chemotherapy, aiming to reach minimal disease burden revealed by PET scan and CEA. Patients with no detectable disease or irreversible treatment-induced liver injury undergo transplant. RESULTS: Nine patients received liver transplant out of 27 who were evaluated (33.3%). Median follow-up was 700 days. Seven patients (77.8%) received a living donor LT. Five had no detectable disease and four had treatment-induced cirrhosis. Pre-transplant management included chemotherapy (n=9) +/- Bevacizumab (n=6) and/or Anti-EGFR (n=6). Median pre-LT cycles of chemotherapy=16 (Range 10-40). Liver-directed therapy included Yttrium-90 (n=5), ablation (n=4), resection (n=4), and HAI-pump (n=3). Three patients recurred after LT. Actuarial 1- and 2-year recurrence-free survival were 75% (n=6/8) and 60% (n=3/5). Recurrence occurred in the lungs (n=1), liver graft (n=1), and lungs+paraaortic nodes (n=1). Patients with pre-LT detectable disease had reduced RFS (p=0.04). All patients with recurrence had histologically-viable tumor in the liver explant. Patients treated in our protocol (n=16) demonstrated improved survival versus those who were not candidates (n=11) regardless of transplant status (p=0.01). CONCLUSION: A protocol defined by aggressive pre-transplant liver-directed treatment and transplant for patients with undetectable disease or treatment-induced liver injury may help prevent tumor recurrence.

Impact of Back-to-Base Normothermic Machine Perfusion on Complications and Costs: A Multi-Center, Real-World Risk-Matched Analysis.

OBJECTIVE: Assess cost and complication outcomes after liver transplantation (LT) using normothermic machine perfusion (NMP). SUMMARY BACKGROUND DATA: End-ischemic NMP is often used to aid logistics, yet its' impact on outcomes after LT remains unclear, as does its' true impact on costs associated with transplantation. METHODS: Deceased donor liver recipients at two centers (1/1/2019-6/30/2023) were included. Retransplants, splits and combined grafts were excluded. End-ischemic NMP (OrganOx-Metra®) was implemented 10/2022 for extended-criteria DBDs, all DCDs and logistics. NMP-cases were matched 1:2 with cold storage controls (SCS) using the Balance-of-Risk (DBD-grafts) and UK-DCD Score (DCD-grafts). RESULTS: Overall, 803 transplantations were included, 174 (21.7%) receiving NMP. Matching was achieved between 118 NMP-DBDs with 236 SCS; and 37 NMP-DCD with 74 corresponding SCS. For both graft types, median inpatient comprehensive complications index (CCI) values were comparable between groups. DCD-NMP grafts experienced reduced cumulative 90-day CCI (27.6 vs. 41.9, P=0.028). NMP also reduced the need for early relaparotomy and renal-replacement-therapy, with subsequently less-frequent major complications (Clavien-Dindo >IVa). This effect was more pronounced in DCD-transplants. NMP had no protective effect on early biliary complications. Organ acquisition/preservation costs were higher with NMP, yet NMP-treated grafts had lower 90-day pre-transplant costs in context of shorter waiting-list times. Overall costs were comparable for both cohorts. CONCLUSIONS: This is the first risk-adjusted outcome and cost analysis comparing NMP and SCS. In addition to logistical benefits, NMP was associated with a reduction in relaparotomy and bleeding in DBD-grafts, and overall complications and post-LT renal-replacement for DCDs. While organ acquisition/preservation was more costly with NMP, overall 90-day-healthcare costs-per-transplantation were comparable.

Emerging and Clinically Accepted Biomarkers for Hepatocellular Carcinoma.

Hepatocellular carcinoma (HCC) is the third leading cause of cancer-related death and the sixth most diagnosed malignancy worldwide. Serum alpha-fetoprotein (AFP) is the traditional, ubiquitous biomarker for HCC. However, there has been an increasing call for the use of multiple biomarkers to optimize care for these patients. AFP, AFP-L3, and prothrombin induced by vitamin K absence II (DCP) have described clinical utility for HCC, but unfortunately, they also have well established and significant limitations. Circulating tumor DNA (ctDNA), genomic glycosylation, and even totally non-invasive salivary metabolomics and/or micro-RNAS demonstrate great promise for early detection and long-term surveillance, but still require large-scale prospective validation to definitively validate their clinical validity. This review aims to provide an update on clinically available and emerging biomarkers for HCC, focusing on their respective clinical strengths and weaknesses.

Circulating Tumor DNA Profiling in Liver Transplant for Hepatocellular Carcinoma, Cholangiocarcinoma, and Colorectal Liver Metastases: A Programmatic Proof of Concept.

INTRODUCTION: Circulating tumor DNA (ctDNA) is emerging as a promising, non-invasive diagnostic and surveillance biomarker in solid organ malignancy. However, its utility before and after liver transplant (LT) for patients with primary and secondary liver cancers is still underexplored. METHODS: Patients undergoing LT for hepatocellular carcinoma (HCC), cholangiocarcinoma (CCA), and colorectal liver metastases (CRLM) with ctDNA testing were included. CtDNA testing was conducted pre-transplant, post-transplant, or both (sequential) from 11/2019 to 09/2023 using Guardant360, Guardant Reveal, and Guardant360 CDx. RESULTS: 21 patients with HCC (n = 9, 43%), CRLM (n = 8, 38%), CCA (n = 3, 14%), and mixed HCC/CCA (n = 1, 5%) were included in the study. The median follow-up time was 15 months (range: 1-124). The median time from pre-operative testing to surgery was 3 months (IQR: 1-4; range: 0-5), and from surgery to post-operative testing, it was 9 months (IQR: 2-22; range: 0.4-112). A total of 13 (62%) patients had pre-transplant testing, with 8 (62%) having ctDNA detected (ctDNA+) and 5 (32%) not having ctDNA detected (ctDNA-). A total of 18 (86%) patients had post-transplant testing, 11 (61%) of whom were ctDNA+ and 7 (33%) of whom were ctDNA-. The absolute recurrence rates were 50% (n = 5) in those who were ctDNA+ vs. 25% (n = 1) in those who were ctDNA- in the post-transplant setting, though this difference was not statistically significant (p = 0.367). Six (29%) patients (HCC = 3, CCA = 1, CRLM = 2) experienced recurrence with a median recurrence-free survival of 14 (IQR: 6-40) months. Four of these patients had positive post-transplant ctDNA collected following diagnosis of recurrence, while one patient had positive post-transplant ctDNA collected preceding recurrence. A total of 10 (48%) patients had sequential ctDNA testing, of whom n = 5 (50%) achieved ctDNA clearance (+/-). The remainder were ctDNA+/+ (n = 3, 30%), ctDNA-/- (n = 1, 10%), and ctDNA-/+ (n = 1, 11%). Three (30%) patients showed the acquisition of new genomic alterations following transplant, all without recurrence. Overall, the median tumor mutation burden (TMB) decreased from 1.23 mut/Mb pre-transplant to 0.00 mut/Mb post-transplant. CONCLUSIONS: Patients with ctDNA positivity experienced recurrence at a higher rate than the ctDNA- patients, indicating the potential role of ctDNA in predicting recurrence after curative-intent transplant. Based on sequential testing, LT has the potential to clear ctDNA, demonstrating the capability of LT in the treatment of systemic disease. Transplant providers should be aware of the potential of donor-derived cell-free DNA and improved approaches are necessary to address such concerns.

Intrinsic supercurrent non-reciprocity coupled to the crystal structure of a van der Waals Josephson barrier.

Non-reciprocal electronic transport in a spatially homogeneous system arises from the simultaneous breaking of inversion and time-reversal symmetries. Superconducting and Josephson diodes, a key ingredient for future non-dissipative quantum devices, have recently been realized. Only a few examples of a vertical superconducting diode effect have been reported and its mechanism, especially whether intrinsic or extrinsic, remains elusive. Here we demonstrate a substantial supercurrent non-reciprocity in a van der Waals vertical Josephson junction formed with a Td-WTe2 barrier and NbSe2 electrodes that clearly reflects the intrinsic crystal structure of Td-WTe2. The Josephson diode efficiency increases with the Td-WTe2 thickness up to critical thickness, and all junctions, irrespective of the barrier thickness, reveal magneto-chiral characteristics with respect to a mirror plane of Td-WTe2. Our results, together with the twist-angle-tuned magneto-chirality of a Td-WTe2 double-barrier junction, show that two-dimensional materials promise vertical Josephson diodes with high efficiency and tunability.

Risk assessment in liver transplantation for hepatocellular carcinoma: long-term follow-up of a two-centre experience.

BACKGROUND: Liver transplantation (LT) is a well-established treatment for hepatocellular carcinoma (HCC), but there are ongoing debates regarding outcomes and selection. This study examines the experience of LT for HCC at a high-volume centre. METHODS: A prospectively maintained database was used to identify HCC patients undergoing LT from 2000 to 2020 with more than or equal to 3-years follow-up. Data were obtained from the centre database and electronic medical records. The Metroticket 2.0 HCC-specific 5-year survival scale was calculated for each patient. Kaplan-Meier and Cox-regression analyses were employed assessing survival between groups based on Metroticket score and individual donor and recipient risk factors. RESULTS: Five hundred sixty-nine patients met criteria. Median follow-up was 96.2 months (8.12 years; interquartile range 59.9-147.8). Three-year recurrence-free (RFS) and overall survival (OS) were 88.6% ( n =504) and 86.6% ( n =493). Five-year RFS and OS were 78.9% ( n =449) and 79.1% ( n =450). Median Metroticket 2.0 score was 0.9 (interquartile range 0.9-0.95). Tumour size greater than 3 cm ( P =0.012), increasing tumour number on imaging ( P =0.001) and explant pathology ( P <0.001) was associated with recurrence. Transplant within Milan ( P <0.001) or UCSF criteria ( P <0.001) had lower recurrence rates. Increasing alpha-fetoprotein (AFP)-values were associated with more HCC recurrence ( P <0.001) and reduced OS ( P =0.008). Chemoembolization was predictive of recurrence in the overall population ( P =0.043) and in those outside-Milan criteria ( P =0.038). A receiver-operator curve using Metroticket 2.0 identified an optimal cut-off of projected survival greater than or equal to 87.5% for predicting recurrence. This cut-off was able to predict RFS ( P <0.001) in the total cohort and predict both, RFS ( P =0.007) and OS ( P =0.016) outside Milan. Receipt of donation after brain death (DBD) grafts (55/478, 13%) or living-donor grafts (3/22, 13.6%) experienced better survival rates compared to donation after cardiac death (DCD) grafts ( n =15/58, 25.6%, P =0.009). Donor age was associated with a higher HCC recurrence ( P =0.006). Both total ischaemia time (TIT) greater than 6hours ( P =0.016) and increasing TIT correlated with higher HCC recurrence ( P =0.027). The use of DCD grafts for outside-Milan candidates was associated with increased recurrence ( P =0.039) and reduced survival ( P =0.033). CONCLUSION: This large two-centre analysis confirms favourable outcomes after LT for HCC. Tumour size and number, pre-transplant AFP, and Milan criteria remain important recipient HCC-risk factors. A higher donor risk (i.e. donor age, DCD grafts, ischaemia time) was associated with poorer outcomes.

Update to 'A Contemporary Systematic Review on Liver Transplantation for Unresectable Liver Metastasis of Colorectal Cancer'.

Colorectal cancer is the second most common cause of cancer-related death worldwide, and half of patients present with colorectal liver metastasis (CRLM). Liver transplant (LT) has emerged as a treatment modality for otherwise unresectable CRLM. Since the publication of the Lebeck-Lee systematic review in 2022, additional evidence has come to light supporting LT for CRLM in highly selected patients. This includes reports of >10-year follow-up with over 80% survival rates in low-risk patients. As these updated reports have significantly changed our collective knowledge, this article is intended to serve as an update to the 2022 systematic review to include the most up-to-date evidence on the subject.

Impact of autotransfusion on recurrence of colorectal cancer liver metastasis: Long-term follow-up of patients undergoing curative intent hepatectomy.

INTRODUCTION: Colorectal cancer liver metastasis (CRLM) occurs in upto 50% of cases and drives patient outcomes. Up-front liver resection is the treatment of choice in resectable cases. There is no consensus yet established as to the safety of intraoperative autotransfusion in liver resection for CRLM. METHODS: Patients undergoing curative-intent hepatectomy for CRLM at a single quaternary-care institution from 1999 to 2016 were included. Demographics, surgical variables, Fong Clinical Risk Score (FCRS), use of intraoperative auto and/or allotransfusion, and survival data were analyzed. Propensity score matching (PSM) was performed accounting for allotransfusion, extent of hepatectomy, FCRS, and systemic treatment regimens. RESULTS: Three-hundred sixteen patients were included. The median follow-up was 10.4 years (7.8-14.1 years). The median recurrence-free survival (RFS) and overall survival (OS) in all patients were 1.6 years (interquartile range: 0.63-6.6 years) and 4.4 years (2.1-8.7), respectively.  Before PSM, there was a significantly reduced RFS in the autotransfusion group (0.96 vs. 1.73 years, p = 0.20). There was no difference in OS (4.11 vs. 4.44 years, p = 0.118). Patients in groups of FCRS 0-2 and 3-5 both had reduced RFS when autotransfusion was used (p = 0.005). This reduction in RFS was further found when comparing autotransfusion versus no autotransfusion within the FCRS 0-2 group and within the FCRS 3-5 group (p = 0.027). On Cox-regression analysis, autotransfusion (hazard ratio = 1.423, 1.028-2.182, p = 0.015) remained predictive of RFS. After PSM, there were no differences in FCRS (p = 0.601), preoperative hemoglobin (p = 0.880), allotransfusion (p = 0.130), adjuvant chemotherapy (p = 1.000), immunotherapy (p = 0.172), tumor grade (p = 1.000), use of platinum-based chemotherapy (p = 0.548), or type of hepatic resection (p = 0.967). After matching, there was a higher rate of recurrence with autotransfusion (69.0% vs. 47.6%, p = 0.046). There was also a reduced time to recurrence in the autotransfusion group compared with the group without (p = 0.006). There was no difference in OS after PSM (p = 0.262). CONCLUSION: Autotransfusion may adversely affect recurrence in liver resection for CRLM. Until further studies clarify this risk profile, the use of intraoperative autotransfusion should be critically assessed on a case-by-case basis only when other resuscitation options are not available.

Combined Liver Transplant and Cardiac Surgery: Long-Term Outcomes and Predictors of Success.

OBJECTIVE: We aim to report our institutional outcomes of single-staged combined liver transplantation (LT) and cardiac surgery (CS). SUMMARY BACKGROUND DATA: Concurrent LT and CS is a potential treatment for combined cardiac dysfunction and end-stage liver disease, yet only 54 cases have been previously reported in the literature. Thus, the outcomes of this approach are relatively unknown, and this approach has been previously regarded as extremely risky. METHODS: Thirty-one patients at our institution underwent combined cardiac surgery and liver transplant. Patients with at least one-year follow-up were included. The Leave-One-Out Cross-Validation (LOOCV) machine-learning approach was used to generate a model for mortality. RESULTS: Median follow-up was 8.2 years (IQR 4.6-13.6 y). One- and five-year survival was 74.2% (N=23) and 55% (N=17), respectively. Negative predictive factors of survival included recipient age>60 years (P=0.036), NASH-cirrhosis (P=0.031), Coronary Artery Bypass-Graft (CABG)-based CS (P=0.046) and pre-operative renal dysfunction (P=0.024). The final model demonstrated that renal dysfunction had a relative weighted impact of 3.2 versus CABG (1.7), age ≥60y (1.7) or NASH (1.3). Elevated LT+CS risk score was associated with an increased five-year mortality after surgery (AUC=0.731, P=<0.001). Conversely, the widely accepted STS-PROM calculator was unable to successfully stratify patients according to 1- (P>0.99) or 5-year (P=0.695) survival rates. CONCLUSIONS: This is the largest series describing combined LT+CS, with joint surgical management appearing feasible in highly selected patients. CABG and pre-operative renal dysfunction are important negative predictors of mortality. The four-variable LT+CS score may help predict patients at high risk for post-operative mortality.

Comparing Outcomes of Minimally Invasive and Open Hepatectomy for Primary Liver Malignancies in Patients with Low-MELD Cirrhosis.

INTRODUCTION: Cirrhotic patients with primary liver cancer may undergo curative-intent resection when selected appropriately. Patients with T1 tumors and low-MELD are generally referred for resection. We aim to evaluate whether minimally invasive hepatectomy (MIH) is associated with improved outcomes versus open hepatectomy (OH). METHODS: NSQIP hepatectomy database 2014-2021 was used to select patients with T1 Hepatocellular Carcinoma (HCC) or Intra-hepatic Cholangiocarcionoma (IHCC) and low-MELD cirrhosis (MELD ≤ 10) who underwent partial hepatectomy. Propensity score matching was applied between OH and MIH patients, and 30-day postoperative outcomes were compared. Multivariable regression was used to identify predictors of post-hepatectomy liver failure (PHLF) in the selected population. RESULTS: There were 922 patients: 494 (53.6%) OH, 372 (40.3%) MIH, and 56 (6.1%) began MIH converted to OH (analyzed with the OH cohort). We matched 354 pairs of patients with an adequate balance between the groups. MIH was associated with lower rates of bile leak (HR 0.37 [0.19-0.72)], PHLF (HR 0.36 [0.15-0.86]), collections requiring drainage (HR 0.30 [0.15-0.63]), postoperative transfusion (HR 0.36 [0.21-0.61]), major (HR 0.45 [0.27-0.77]), and overall morbidity (HR 0.44 [0.31-0.63]), and a two-day shorter median hospitalization (3 vs. 5 days; HR 0.61 [0.45-0.82]). No difference was noted in operative time, wound, respiratory, and septic complications, or mortality. Regression analysis identified ascites, prior portal vein embolization (PVE), additional hepatectomies, Pringle's maneuver, and OH (vs. MIH) as independent predictors of PHLF. CONCLUSION: MIH for early-stage HCC/IHCC in low-MELD cirrhotic patients was associated with improved postoperative outcomes over OH. These findings suggest that MIH should be considered an acceptable approach in this population of patients.

Chiral antiferromagnetic Josephson junctions as spin-triplet supercurrent spin valves and d.c. SQUIDs.

Spin-triplet supercurrent spin valves are of practical importance for the realization of superconducting spintronic logic circuits. In ferromagnetic Josephson junctions, the magnetic-field-controlled non-collinearity between the spin-mixer and spin-rotator magnetizations switches the spin-polarized triplet supercurrents on and off. Here we report an antiferromagnetic equivalent of such spin-triplet supercurrent spin valves in chiral antiferromagnetic Josephson junctions as well as a direct-current superconducting quantum interference device. We employ the topological chiral antiferromagnet Mn3Ge, in which the Berry curvature of the band structure produces fictitious magnetic fields, and the non-collinear atomic-scale spin arrangement accommodates triplet Cooper pairing over long distances (>150 nm). We theoretically verify the observed supercurrent spin-valve behaviours under a small magnetic field of <2 mT for current-biased junctions and the direct-current superconducting quantum interference device functionality. Our calculations reproduce the observed hysteretic field interference of the Josephson critical current and link these to the magnetic-field-modulated antiferromagnetic texture that alters the Berry curvature. Our work employs band topology to control the pairing amplitude of spin-triplet Cooper pairs in a single chiral antiferromagnet.

Reduced dopant-induced scattering in remote charge-transfer-doped MoS2 field-effect transistors.

Efficient doping for modulating electrical properties of two-dimensional (2D) transition metal dichalcogenide (TMDC) semiconductors is essential for meeting the versatile requirements for future electronic and optoelectronic devices. Because doping of semiconductors, including TMDCs, typically involves generation of charged dopants that hinder charge transport, tackling Coulomb scattering induced by the externally introduced dopants remains a key challenge in achieving ultrahigh mobility 2D semiconductor systems. In this study, we demonstrated remote charge transfer doping by simply inserting a hexagonal boron nitride layer between MoS2 and solution-deposited n-type dopants, benzyl viologen. A quantitative analysis of temperature-dependent charge transport in remotely doped devices supports an effective suppression of the dopant-induced scattering relative to the conventional direct doping method. Our mechanistic investigation of the remote doping method promotes the charge transfer strategy as a promising method for material-level tailoring of electrical and optoelectronic devices based on TMDCs.

Zero-field polarity-reversible Josephson supercurrent diodes enabled by a proximity-magnetized Pt barrier.

Simultaneous breaking of inversion and time-reversal symmetries in a conductor yields a non-reciprocal electronic transport1-3, known as the diode or rectification effect, that is, low (ideally zero) conductance in one direction and high (ideally infinite) conductance in the other. So far, most of the diode effects observed in non-centrosymmetric polar/superconducting conductors4-7 and Josephson junctions8-10 require external magnetic fields to break the time-reversal symmetry. Here we report zero-field polarity-switchable Josephson supercurrent diodes, in which a proximity-magnetized Pt layer by ferrimagnetic insulating Y3Fe5O12 serves as the Rashba(-type) Josephson barrier. The zero-field diode efficiency of our proximity-engineered device reaches up to ±35% at 2 K, with a clear square-root dependence on temperature. Measuring in-plane field-strength/angle dependences and comparing with Cu-inserted control junctions, we demonstrate that exchange spin-splitting11-13 and Rashba(-type) spin-orbit coupling13-15 at the Pt/Y3Fe5O12 interface are key for the zero-field giant rectification efficiency. Our achievement advances the development of field-free absolute Josephson diodes.

Enhanced Thermoelectric Power Factor in Carrier-Type-Controlled Platinum Diselenide Nanosheets by Molecular Charge-Transfer Doping.

2D transition metal dichalcogenides (TMDCs) have revealed great promise for realizing electronics at the nanoscale. Despite significant interests that have emerged for their thermoelectric applications due to their predicted high thermoelectric figure of merit, suitable doping methods to improve and optimize the thermoelectric power factor of TMDCs have not been studied extensively. In this respect, molecular charge-transfer doping is utilized effectively in TMDC-based nanoelectronic devices due to its facile and controllable nature owing to a diverse range of molecular designs available for modulating the degree of charge transfer. In this study, the power of molecular charge-transfer doping is demonstrated in controlling the carrier-type (n- and p-type) and thermoelectric power factor in platinum diselenide (PtSe2 ) nanosheets. This, combined with the tunability in the band overlap by changing the thickness of the nanosheets, allows a significant increase in the thermoelectric power factor of the n- and p-doped PtSe2 nanosheets to values as high as 160 and 250 µW mK-2 , respectively. The methodology employed in this study provides a simple and effective route for the molecular doping of TMDCs that can be used for the design and development of highly efficient thermoelectric energy conversion systems.

Channel-Length-Modulated Avalanche Multiplication in Ambipolar WSe2 Field-Effect Transistors.

Recently there has been growing interest in avalanche multiplication in two-dimensional (2D) materials and device applications such as avalanche photodetectors and transistors. Previous studies have mainly utilized unipolar semiconductors as the active material and focused on developing high-performance devices. However, fundamental analysis of the multiplication process, particularly in ambipolar materials, is required to establish high-performance electronic devices and emerging architectures. Although ambipolar 2D materials have the advantage of facile carrier-type tuning through electrostatic gating, simultaneously allowing both carrier types in a single channel poses an inherent difficulty in analyzing their individual contributions to avalanche multiplication. In ambipolar field-effect transistors (FETs), two phenomena of ambipolar transport and avalanche multiplication can occur, and both exhibit secondary rise of output current at high lateral voltage. We distinguished these two competing phenomena using the method of channel length modulation and successfully analyzed the properties of electron- and hole-initiated multiplication in ambipolar WSe2 FETs. Our study provides a simple and robust method to examine carrier multiplication in ambipolar materials and will foster the development of high-performance atomically thin electronic devices utilizing avalanche multiplication.

Role of Two-Dimensional Ising Superconductivity in the Nonequilibrium Quasiparticle Spin-to-Charge Conversion Efficiency.

Nonequilibrium studies of two-dimensional (2D) superconductors (SCs) with Ising spin-orbit coupling are prerequisite for their successful application to equilibrium spin-triplet Cooper pairs and, potentially, Majorana Fermions. By taking advantage of the recent discoveries of 2D SCs and their compatibility with any other materials, we fabricate here nonlocal magnon devices to examine how such 2D Ising superconductivity affects the conversion efficiency of magnon spin to quasiparticle charge in superconducting flakes of 2H-NbSe2 transferred onto ferrimagnetic insulating Y3Fe5O12. Comparison with a reference device based on a conventionally paired superconductor shows that the Y3Fe5O12-induced in-plane (IP) exchange spin-splitting in the NbSe2 flake is hindered by its inherent out-of-plane (OOP) spin-orbit field, which, in turn, limits the transition-state enhancement of the spin-to-charge conversion efficiency. Our out-of-equilibrium study highlights the significance of symmetry matching between underlying Cooper pairs and exchange-induced spin-splitting for the giant transition-state spin-to-charge conversion and may have implications toward proximity-engineered spin-polarized triplet pairing via tuning the relative strength of IP exchange and OOP spin-orbit fields in ferromagnetic insulator/2D Ising SC bilayers.

Molecular Dopant-Dependent Charge Transport in Surface-Charge-Transfer-Doped Tungsten Diselenide Field Effect Transistors.

The controllability of carrier density and major carrier type of transition metal dichalcogenides(TMDCs) is critical for electronic and optoelectronic device applications. To utilize doping in TMDC devices, it is important to understand the role of dopants in charge transport properties of TMDCs. Here, the effects of molecular doping on the charge transport properties of tungsten diselenide (WSe2 ) are investigated using three p-type molecular dopants, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4 -TCNQ), tris(4-bromophenyl)ammoniumyl hexachloroantimonate (magic blue), and molybdenum tris(1,2-bis(trifluoromethyl)ethane-1,2-dithiolene) (Mo(tfd-COCF3 )3 ). The temperature-dependent transport measurements show that the dopant counterions on WSe2 surface can induce Coulomb scattering in WSe2 channel and the degree of scattering is significantly dependent on the dopant. Furthermore, the quantitative analysis revealed that the amount of charge transfer between WSe2 and dopants is related to not only doping density, but also the contribution of each dopant ion toward Coulomb scattering. The first-principles density functional theory calculations show that the amount of charge transfer is mainly determined by intrinsic properties of the dopant molecules such as relative frontier orbital positions and their spin configurations. The authors' systematic investigation of the charge transport of doped TMDCs will be directly relevant for pursuing molecular routes for efficient and controllable doping in TMDC nanoelectronic devices.