Robust Surface States and Coherence Phenomena in Magnetically Alloyed SmB_{6}.

Samarium hexaboride is a candidate for the topological Kondo insulator state, in which Kondo coherence is predicted to give rise to an insulating gap spanned by topological surface states. Here we investigate the surface and bulk electronic properties of magnetically alloyed Sm_{1-x}M_{x}B_{6} (M=Ce, Eu), using angle-resolved photoemission spectroscopy and complementary characterization techniques. Remarkably, topologically nontrivial bulk and surface band structures are found to persist in highly modified samples with up to 30% Sm substitution and with an antiferromagnetic ground state in the case of Eu doping. The results are interpreted in terms of a hierarchy of energy scales, in which surface state emergence is linked to the formation of a direct Kondo gap, while low-temperature transport trends depend on the indirect gap.

Application of emitter-sample hybrid terahertz time-domain spectroscopy to investigate temperature-dependent optical constants of doped InAs.

We investigate temperature-dependent carrier dynamics of InAs crystal by using reflection-type terahertz time-domain spectroscopy, particularly with a recently developed emitter-sample hybrid structure. We successfully obtain the optical conductivity in a terahertz frequency of bulk InAs whose dc conductivity is in the range of 100-150 Ω-1 cm-1. We find that both real and imaginary parts of the optical conductivity can be fit well with the simple Drude model, and the free-carrier density and the scattering rate obtained from the fit are in good agreement with corresponding values obtained by using other techniques, such as the Hall measurement and the dc-resistivity measurement. These results clearly demonstrate that the proposed technique of adopting the emitter-sample hybrid structure can be exploited to determine temperature-dependent optical constants in a reflection geometry and hence to investigate electrodynamics of bulk metallic systems.

Observation of Orbital Order in the Half-Filled 4f Gd Compound.

Half-filled electron systems, even with the maximized spin angular moment, have been given little attention because of their zero-orbital angular moment according to Hund's rule. Nevertheless, there are several measurements that show evidence of a nonzero orbital moment as well as spin-orbit coupling. Here we report for the first time the orbital order in a half-filled 4f-electron system GdB_{4}, using the resonant soft x-ray scattering at Gd M_{4,5}-edges. Furthermore, we discovered that the development of this orbital order is strongly coupled with the antiferromagnetic spin order. These results clearly demonstrate that even in half-filled electron systems the orbital angular moment can be an important parameter to describe material properties, and may provide significant opportunities for tailoring new correlated electron systems.

Electronic Structure of YbB_{6}: Is it a Topological Insulator or Not?

To finally resolve the controversial issue of whether or not the electronic structure of YbB_{6} is nontrivially topological, we have made a combined study using angle-resolved photoemission spectroscopy (ARPES) of the nonpolar (110) surface and density functional theory (DFT). The flat-band conditions of the (110) ARPES avoid the strong band bending effects of the polar (001) surface and definitively show that YbB_{6} has a topologically trivial B 2p-Yb 5d semiconductor band gap of ∼0.3 eV. Accurate determination of the low energy band topology in DFT requires the use of a modified Becke-Johnson exchange potential incorporating spin-orbit coupling and an on-site Yb 4f Coulomb interaction U as large as 7 eV. The DFT result, confirmed by a more precise GW band calculation, is similar to that of a small gap non-Kondo nontopological semiconductor. Additionally, the pressure-dependent electronic structure of YbB_{6} is investigated theoretically and found to transform into a p-d overlap semimetal with small Yb mixed valency.

Importance of charge fluctuations for the topological phase in SmB(6).

Typical Kondo insulators (KIs) can have a nontrivial Z_{2} topology because the energy gap opens at the Fermi energy (E_{F}) by a hybridization between odd- and even-parity bands. SmB_{6} deviates from such KI behavior, and it has been unclear how the insulating phase occurs. Here, we demonstrate that charge fluctuations are the origin of the topological insulating phase in SmB_{6}. Our angle-resolved photoemission spectroscopy results reveal that with decreasing temperature the bottom of the d-f hybridized band at the X[over ¯] point, which is predicted to have odd parity and is required for a topological phase, gradually shifts from below to above E_{F}. We conclude that SmB_{6} is a charge-fluctuating topological insulator.

Intermediate valence state in YbB4revealed by resonant x-ray emission spectroscopy.

We report the temperature dependence of the Yb valence in the geometrically frustrated compoundYbB4from 12 to 300 K using resonant x-ray emission spectroscopy at the YbLα1transition. We find that the Yb valence,v, is hybridized between thev = 2 andv = 3 valence states, increasing fromv=2.61±0.01at 12 K tov=2.67±0.01at 300 K, confirming thatYbB4is a Kondo system in the intermediate valence regime. This result indicates that the Kondo interaction inYbB4is substantial, and is likely to be the reason whyYbB4does not order magnetically at low temperature, rather than this being an effect of geometric frustration. Furthermore, the zero-point valence of the system is extracted from our data and compared with other Kondo lattice systems. The zero-point valence seems to be weakly dependent on the Kondo temperature scale, but not on the valence change temperature scaleTv.

Increased immunoreactivity of membrane type-1 matrix metalloproteinase (MT1-MMP) and ß-catenin in high-risk basal cell carcinoma.

BACKGROUND: Although various immunohistological markers have been investigated to assess the aggressive characteristics of basal cell carcinoma (BCC), the role of membrane type-1 matrix metalloproteinase (MT1-MMP) has not been well established. OBJECTIVES: To clarify the precise role of MT1-MMP in BCC, MT1-MMP expression was studied in various histological subtypes of BCC. MATERIALS AND METHODS: High-risk subtypes of BCC were compared by assessing the expression of ß-catenin and MT1-MMP. The tissue microarray technique was used for immunohistochemical staining. Fifty-eight samples were divided into six subtypes (10 nodular, 12 mixed, nine infiltrative, eight morphoeiform, 10 micro-nodular and nine basosquamous). Overall, the 10 nodular BCC samples were classified as low-risk BCC and the remaining 48 samples were classified as high-risk BCCs. RESULTS: ß-Catenin immunoreactivity was increased in the high-risk BCCs compared with the low-risk (nodular) BCC (P < 0·001). Nuclear ß-catenin immunoreactivity was increased at the invading front of mixed BCC tumour islands compared with the upper portion of the lesion (P < 0·01). For the mixed BCC (P < 0·01), infiltrative BCC (P < 0·001), morphoeiform BCC (P < 0·001), micronodular BCC (P < 0·001) and basosquamous (P < 0·001) carcinoma, ß-catenin immunoreactivity was increased at the invading front compared with nodular BCC. MT1-MMP immunoreactivity was increased in the high-risk BCCs compared with the low-risk (nodular) BCC (P < 0·01). The membranous MT1-MMP immunoreactivity was increased at the invading front of mixed BCC tumour islands compared with the upper portion of the lesions (P < 0·01). For the mixed (P < 0·01), infiltrative (P < 0·05), morphoeiform (P < 0·05), micronodular (P > 0·05) and basosquamous (P < 0·05) BCC, MT1-MMP immunoreactivity was also increased at the invading front compared with nodular BCC. CONCLUSIONS: The results of this study suggest that MT1-MMP might be a novel marker for high-risk BCC. In addition, expression of both ß-catenin and MT1-MMP was increased in high-risk BCC tumour cells, indicating that these two proteins may play an important role in locally invasive and highly destructive growth behaviour of high-risk BCCs.

Pinning characteristics of domain wall in giant magnetoresistance spin valve stripe, consisting of a nano-wire and a circular ring.

We investigated a technique for proving the pinning behaviors of a domain wall (DW) in spin-valve stripes with artificial configurations, which consist of a nano-wire, a large pad and sharp tip at the ends of the wire, and a circular ring at the center. It was found from the GMR measurement at various positions that a DW was pinned at a ring during DW's propagation from the side of pad to the side of tip. Micromagnetic simulation revealed that the initial onion magnetic states of the ring changes continuously to final reverse onion state via counterclockwise vortex state when a counterclockwise tail-to-tail DW pass through the ring. In addition, the simulation results indicated that the magnetic states at a circular ring were determined by the type and chirality of DW. We also studied the characteristics of domain wall motion in the same configuration, when the nano-ring was replaced with square and diamond structures.

Parametric excitation and mode control using an Oersted field in a NiFe nanowire.

Parametric pumping is a nonlinear wave phenomenon and a promising technique for electronic devices based on spin waves, so-called "magnonics". For parametric excitation, a magnetic nanowire system that has a built-in dc current line to produce an Oersted field is designed, and for spin wave detection, a micro-Brillouin light scattering (µ-BLS) system is used. A spin wave with a frequency of fsw = 5.6 GHz is observed when a pumping microwave with a frequency of fmw = 11.2 GHz is applied. The wave is found to be of the n = 1 width mode (n is the antinode number), and its mode changes to an edge-localized (or possibly n > 1) mode when the Oersted field (or current) varies. Joule heating effects are not observed in the pumping process. Thus, spin wave mode control by the built-in current would be a convenient and useful method to enhance the efficiency and compatibility in applications of spin-based electronics.

Tunable asymmetric spin wave excitation and propagation in a magnetic system with two rectangular blocks.

Asymmetric spin wave excitation and propagation are key properties to develop spin-based electronics, such as magnetic memory, spin information and logic devices. To date, such nonreciprocal effects cannot be manipulated in a system because of the geometrical magnetic configuration, while large values of asymmetry ratio are achieved. In this study, we suggest a new magnetic system with two blocks, in which the asymmetric intensity ratio can be changed between 0.276 and 1.43 by adjusting the excitation frequency between 7.8 GHz and 9.4 GHz. Because the two blocks have different widths, they have their own spin wave excitation frequency ranges. Indeed, the spin wave intensities in the two blocks, detected by the Brillouin light scattering spectrum, were observed to be frequency-dependent, yielding tuneable asymmetry ratio. Thus, this study provides a new path to enhance the application of spin waves in spin-based electronics.

Homeostasis-stimulated proliferation drives naive T cells to differentiate directly into memory T cells.

The developmental requirements for immunological memory, a central feature of adaptive immune responses, is largely obscure. We show that as naive CD8 T cells undergo homeostasis-driven proliferation in lymphopenic mice in the absence of overt antigenic stimulation, they progressively acquire phenotypic and functional characteristics of antigen-induced memory CD8 T cells. Thus, the homeostasis-induced memory CD8 T cells express typical memory cell markers, lyse target cells directly in vitro and in vivo, respond to lower doses of antigen than naive cells, and secrete interferon gamma faster upon restimulation. Like antigen-induced memory T cell differentiation, the homeostasis-driven process requires T cell proliferation and, initially, the presence of appropriate restricting major histocompatibility complexes, but it differs by occurring without effector cell formation and without requiring interleukin 2 or costimulation via CD28. These findings define repetitive cell division plus T cell receptor ligation as the basic requirements for naive to memory T cell differentiation.

CD8(-) T cell transfectants that express a high affinity T cell receptor exhibit enhanced peptide-dependent activation.

T cells are activated by binding of the T cell receptor (TCR) to a peptide-major histocompatibility complex (MHC) complex (pMHC) expressed on the surface of antigen presenting cells. Various models have predicted that activation is limited to a narrow window of affinities (or dissociation rates) for the TCR-pMHC interaction and that above or below this window, T cells will fail to undergo activation. However, to date there have not been TCRs with sufficiently high affinities in order to test this hypothesis. In this report we examined the activity of a CD8-negative T cell line transfected with a high affinity mutant TCR (K(D) = 10 nM) derived from cytotoxic T lymphocyte clone 2C by in vitro engineering. The results show that despite a 300-fold higher affinity and a 45-fold longer off-rate compared with the wild-type TCR, T cells that expressed the mutant TCRs were activated by peptide. In fact, activation could be detected at significantly lower peptide concentrations than with T cells that expressed the wild-type TCR. Furthermore, binding and functional analyses of a panel of peptide variants suggested that pMHC stability could account for apparent discrepancies between TCR affinity and T cell activity observed in several prior studies.

The antimicrobial peptide human cationic antimicrobial protein-18/cathelicidin LL-37 as a putative growth factor for malignant melanoma.

BACKGROUND: Recent evidence suggests cathelicidin LL-37 to be a growth factor for various human cancers such as lung cancer, ovarian cancer and breast cancer. However, the effect of LL-37 against malignant skin cancer has not been reported. OBJECTIVES: To investigate whether the human cathelicidin LL-37 is involved in the carcinogenesis of various skin tumours. METHODS: Human cationic antimicrobial protein-18 (hCAP-18)/LL-37 production in several cell lines including HaCaT, a chronic myelogenous leukaemia (CML) cell line and various melanoma cell lines was examined using reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay. Immunohistochemical analysis of melanoma, nonmelanoma skin cancer and precancerous and benign skin lesions was performed. After adding LL-37 to a melanoma cell line, tumour cell proliferation, migration and invasion were investigated. RESULTS: Human malignant melanoma cell lines overexpressed hCAP-18/LL-37 mRNA and peptide compared with HaCaT and CML cell lines. Immunohistochemistry showed that the peptide was strongly expressed in malignant melanoma and moderately expressed in squamous cell carcinoma, whereas basal cell carcinoma, precancerous lesions and seborrhoeic keratosis showed no or weak expression. LL-37 also stimulated melanoma cell proliferation, migration and invasion in vitro. CONCLUSIONS: Cathelicidin LL-37 was primarily expressed in human malignant skin cancer. LL-37 promoted melanoma cell proliferation, migration and invasion in vitro. We report that an increase in the level of LL-37 is associated with malignant skin tumours such as malignant melanoma. These results highlight the importance of LL-37 in the malignant tendency of skin tumours.

Spitz naevus is rare in Korea.

BACKGROUND: Spitz naevi have not been widely studied in Asians. AIM: To compare the epidemiology and clinicopathological features of Spitz naevi in Koreans with lesions in western countries. METHODS: In total, 80 Spitz naevi in 77 patients diagnosed over 10 years at 17 university hospitals in Korea were analysed. RESULTS: The relative incidence of Spitz naevus vs. MM was 1 vs. 10.9. In most patients (75%) the Spitz naevi had been present for > 6 months. The size of the lesion was relatively large. Histologically, most of the lesions (54%) were the dermal type and pigmentation was common (49% of lesions). Immunohistochemical study found that all of the 34 lesions were positive for S-100 protein but only 14 (47%) were positive for HMB-45. CONCLUSION: Spitz naevus is rare in Korea. The lesions were more commonly larger, pigmented, and of the dermal type than reported in western countries.

Quadrupolar ordering and exotic magnetocaloric effect in RB4 (R = Dy, Ho).

The interplay of charge, spin, orbital and lattice degrees of freedom has recently received great interest due to its potential to improve the magnetocaloric effect (MCE) for the purpose of magnetic cooling applications. Here, a new mechanism for a large entropy change with low magnetic fields in rare-earth tetraborides, especially for Ho1-xDyxB4 (x = 0.0, 0.5, and 1.0), is proposed. For x = 0.0, 0.5, and 1.0, the maximum entropy changes of the giant inverse MCE are found to be 22.7 J/kgK, 19.6 J/kgK, and 19.0 J/kgK with critical fields of 25 kOe, 40 kOe, and 50 kOe, respectively. For all compounds, systematic study on how the entropy changes as a function of the field and temperature is performed to investigate their correlation with consecutive double transitions, i.e., the magnetic dipolar order at T = TN and the quadrupolar order at T = TQ (TQ < TN). Based on Landau theory, it is found that this behaviour is attributed to the strong coupling between magnetic dipoles and quadrupoles in the presence of strong spin-orbit coupling and geometric frustration. Our work offers new insights into both academic and industrial interests in the discovery of giant MCE with various applications for magnetic cooling systems.

Current-induced domain wall nucleation and its pinning characteristics at a notch in a spin-valve nanowire.

The characteristics of domain wall (DW) pinning at a notch in a spin-valve nanowire were investigated when a DW was created by a current, flowing into a spin-valve nanowire. It was found that DW pinning at a notch is quite sensitive to the magnitude of the current and its polarity. The current-polarity dependence of DW pinning is likely due to the spin structure in the core of the DW, which is determined by an Oersted field from the current in a Cu layer. This indicates that the control of DW pinning at a notch in a nanowire can be achieved by a current acting on its own, which is an important advantage of this method, compared with field-induced DW control.

Current-induced magnetic switching with spin-orbit torque in an interlayer-coupled junction with a Ta spacer layer.

Spin-orbit torque has attracted considerable attention as a means to overcome limits of devices based on spin-transfer torque. However, a small magnetic field that is collinear to the current flow must be applied to break symmetry and induce deterministic current-induced magnetization switching. Recently, a junction utilizing interlayer coupling mediated by a Ru spacer layer between two CoFe layers was designed for symmetry breaking and exhibited current-induced magnetization switching without a magnetic field. Here, we demonstrate zero-field current-induced switching of the perpendicular magnetization of a Co layer that is indirectly coupled with a CoFe layer via a Ta spacer. The weak interlayer coupling exhibited by Ta allows the layer thickness to be relatively small (≈0.5 nm), enabling appropriate interlayer coupling to induce spin-orbit torque for current-induced magnetic switching. External magnetic field effects on switching characteristics show that the current switching process is quite stable against external environments.