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1.
Phys Rev Lett ; 112(23): 236602, 2014 Jun 13.
Article in English | MEDLINE | ID: mdl-24972220

ABSTRACT

We report experimental evidence of a remarkable spontaneous time-reversal symmetry breaking in two-dimensional electron systems formed by atomically confined doping of phosphorus (P) atoms inside bulk crystalline silicon (Si) and germanium (Ge). Weak localization corrections to the conductivity and the universal conductance fluctuations were both found to decrease rapidly with decreasing doping in the Si:P and Ge:P delta layers, suggesting an effect driven by Coulomb interactions. In-plane magnetotransport measurements indicate the presence of intrinsic local spin fluctuations at low doping, providing a microscopic mechanism for spontaneous lifting of the time-reversal symmetry. Our experiments suggest the emergence of a new many-body quantum state when two-dimensional electrons are confined to narrow half-filled impurity bands.


Subject(s)
Electrons , Germanium/chemistry , Models, Chemical , Silicon/chemistry , Electric Conductivity , Phosphorus/chemistry , Quantum Theory
2.
Neurology ; 71(24): 1973-80, 2008 Dec 09.
Article in English | MEDLINE | ID: mdl-19064878

ABSTRACT

BACKGROUND: Autosomal dominant partial epilepsy with auditory features (ADPEAF) is an idiopathic focal epilepsy syndrome with auditory symptoms or receptive aphasia as major ictal manifestations, frequently associated with mutations in the leucine-rich, glioma inactivated 1 (LGI1) gene. Although affected subjects do not have structural abnormalities detected on routine MRI, a lateral temporal malformation was identified through high resolution MRI in one family. We attempted to replicate this finding and to assess auditory and language processing in ADPEAF using fMRI and magnetoencephalography (MEG). METHODS: We studied 17 subjects (10 affected mutation carriers, 3 unaffected carriers, 4 noncarriers) in 7 ADPEAF families, each of which had a different LGI1 mutation. Subjects underwent high-resolution structural MRI, fMRI with an auditory description decision task (ADDT) and a tone discrimination task, and MEG. A control group comprising 26 volunteers was also included. RESULTS: We found no evidence of structural abnormalities in any of the 17 subjects. On fMRI with ADDT, subjects with epilepsy had significantly less activation than controls. On MEG with auditory stimuli, peak 2 auditory evoked field latency was significantly delayed in affected individuals compared to controls. CONCLUSIONS: These findings do not support the previous report of a lateral temporal malformation in autosomal dominant partial epilepsy with auditory features (ADPEAF). However, our fMRI and magnetoencephalography data suggest that individuals with ADPEAF have functional impairment in language processing.


Subject(s)
Auditory Cortex/physiopathology , Auditory Perception/genetics , Epilepsies, Partial/complications , Language Disorders/physiopathology , Speech Perception/genetics , Acoustic Stimulation , Adult , Auditory Cortex/pathology , Brain Mapping , Chromosome Disorders/complications , Chromosome Disorders/genetics , Epilepsies, Partial/genetics , Female , Functional Laterality/genetics , Genes, Dominant/genetics , Humans , Intracellular Signaling Peptides and Proteins , Language Disorders/genetics , Language Disorders/pathology , Language Tests , Magnetic Resonance Imaging , Magnetoencephalography , Male , Mutation/genetics , Proteins/genetics , Reaction Time/genetics
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