Bereziskii-Kosterlitz-Thouless transition in the Weyl system PtBi2

2021 ◽  
Author(s):  
Arthur Veyrat ◽  
Valentin Labracherie ◽  
Rohith Acharya ◽  
Dima Bashlakov ◽  
Federico Caglieris ◽  
...  
Keyword(s):  
Condensed Matter ◽  
Three Dimensional ◽  
Spin Orbit Coupling ◽  
Two Dimensional ◽  
Pairing Mechanism ◽  
Critical Fields ◽  
Weyl Semimetal ◽  
Superconducting Coherence Length ◽  
Low Dimensional ◽  
Strong Spin

Abstract Symmetry breaking in topological matter became, in the last decade, a key concept in condensed matter physics to unveil novel electronic states. In this work, we reveal that broken inversion symmetry and strong spin-orbit coupling in trigonal PtBi2 lead to a Weyl semimetal band structure, with unusually robust two-dimensional superconductivity in thin fims. Transport measurements show that high-quality PtBi2 crystals are three-dimensional superconductors (Tc≈600 mK) with an isotropic critical field (Bc≈50 mT). Remarkably, we evidence in a rather thick flake (60 nm), exfoliated from a macroscopic crystal, the two-dimensional nature of the superconducting state, with a critical temperature Tc≈370 mK and highly-anisotropic critical fields. Our results reveal a Berezinskii-Kosterlitz-Thouless transition with TBKT≈310 mK and with a broadening of Tc due to inhomogenities in the sample. Due to the very long superconducting coherence length ξ in PtBi2, the vortex-antivortex pairing mechanism can be studied in unusually-thick samples (at least five times thicker than for any other two-dimensional superconductor), making PtBi2 an ideal platform to study low dimensional superconductivity in a topological semimetal.

scholarly journals Strong spin depolarization in the ferromagnetic Weyl semimetal Co3Sn2S2 : Role of spin-orbit coupling

2020 ◽  
Vol 102 (10) ◽  
Author(s):  
Sandeep Howlader ◽  
Surabhi Saha ◽  
Ritesh Kumar ◽  
Vipin Nagpal ◽  
Satyabrata Patnaik ◽  
...  
Keyword(s):  
Orbit Coupling ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Weyl Semimetal ◽  
Spin Depolarization ◽  
Strong Spin

Validity of the Free Electron Model for Two-Dimensional Electrodes

2015 ◽  
Vol 1753 ◽  
Author(s):  
Kenji Kondo
Keyword(s):  
Electron Correlation ◽  
Free Electron ◽  
Three Dimensional ◽  
Electron Energy Spectrum ◽  
Careful Consideration ◽  
Two Dimensional ◽  
Electron Gases ◽  
Electron Model ◽  
Free Electron Model ◽  
Low Dimensional

ABSTRACTGenerally, the electrodes are regarded as free electron gases when we calculate the transport characteristics of nanostructure materials or devices. In three dimensional electrodes, there are little electron correlation. However, in low-dimensional electrodes, electron correlation becomes much larger than that in three dimensional ones. Recently, nanotechnology has made much progress to fabricate two-dimensional (2D) electrodes easily and precisely. As a result, we must consider whether two-dimensional electrodes can be regarded as free electron gases. In this study, we investigate the electron energy spectrum of 2D electrodes, taking into consideration the electron correlation. These results suggest that the free electron model is justified only at the Fermi momentum and that we should not regard 2D electrodes as free electron gases without careful consideration under high electric field and/or high temperature.

Statistical Approach to Shape from Shading: Reconstruction of Three-Dimensional Face Surfaces from Single Two-Dimensional Images

1996 ◽  
Vol 8 (6) ◽  
pp. 1321-1340 ◽  
Author(s):  
Joseph J. Atick ◽  
Paul A. Griffin ◽  
A. Norman Redlich
Keyword(s):  
Dimensional Space ◽  
Three Dimensional ◽  
Practical Interest ◽  
Principal Component ◽  
Shape From Shading ◽  
Shape Space ◽  
Two Dimensional ◽  
Two Dimensional Image ◽  
Low Dimensional ◽  
Dimensional Object

The human visual system is proficient in perceiving three-dimensional shape from the shading patterns in a two-dimensional image. How it does this is not well understood and continues to be a question of fundamental and practical interest. In this paper we present a new quantitative approach to shape-from-shading that may provide some answers. We suggest that the brain, through evolution or prior experience, has discovered that objects can be classified into lower-dimensional object-classes as to their shape. Extraction of shape from shading is then equivalent to the much simpler problem of parameter estimation in a low-dimensional space. We carry out this proposal for an important class of three-dimensional (3D) objects: human heads. From an ensemble of several hundred laser-scanned 3D heads, we use principal component analysis to derive a low-dimensional parameterization of head shape space. An algorithm for solving shape-from-shading using this representation is presented. It works well even on real images where it is able to recover the 3D surface for a given person, maintaining facial detail and identity, from a single 2D image of his face. This algorithm has applications in face recognition and animation.

A POSSIBLE PAIRING MECHANISM FOR HTSC: TWO-DIMENSIONAL CONFINEMENT AND COULOMB OVER-SCREENING

1999 ◽  
Vol 13 (29n31) ◽  
pp. 3472-3477 ◽  
Author(s):  
D. ARIOSA ◽  
H. BECK
Keyword(s):  
Mean Field ◽  
Three Dimensional ◽  
Critical Density ◽  
Zero Point ◽  
Coulomb Repulsion ◽  
Two Dimensional ◽  
Pairing Mechanism ◽  
Density Region ◽  
Point Energy ◽  
Localization Energy

Among all the common properties of HTCS cuprates, we build our model on two of them: their high anisotropy, and their extremely low density of charge carriers. The intra-layer pairing mechanism is provided by the two-dimensional over-screening of Coulomb repulsion.1,2 The c-axis zero point energy restricts this pairing to a low carrier density region. Below a critical density, the system behaves as a two-dimensional confined jellium where the energy gain due to charge pairing is larger than the c-axis localization energy. In the high density region, where the pairing energy cannot compensate the localization energy, the system delocalizes and crosses over to a three-dimensional regime. This competition between binding and confinement energies implies a monotonic decrease of mass anisotropy with doping. Pre-formed pairs which exist below a Mean Field (MF) temperature defined by the binding energy, account for pseudo-gap observations.3,4 The superconducting critical temperature T c is given by the Beresinskii–Kosterlitz–Thouless (BKT) transition of the two-dimensional layer, renormalized by quantum phase fluctuations (QPF).5 QPF account for the metal-insulator transition at very low doping.

Fermions in low-dimensional systems and the transition between bulk and surface properties

2008 ◽  
Vol 86 (4) ◽  
pp. 601-610
Author(s):  
R Dick
Keyword(s):  
Surface Properties ◽  
Green's Functions ◽  
Green’S Functions ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Low Dimensional

We discuss three formalisms for the description of Fermions in low-dimensional systems. Then we consider dimensionally hybrid Hamiltonians with mixed three-dimensional and two-dimensional kinetic terms. These Hamiltonians yield particular dimensionally hybrid Green’s functions with interesting prospects for the description of the transition between two-dimensional and three-dimensional behavior of particles in the presence of attractive interface potentials.PACS Nos.: 05.30.Fk, 71.10.Pm, 73.20.–r

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