scholarly journals Excitonic density wave and spin-valley superfluid in bilayer transition metal dichalcogenide

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Zhen Bi ◽  
Liang Fu
Keyword(s):  
Magnetic Field ◽  
Spin Injection ◽  
Twist Angle ◽  
Density Wave ◽  
Transition Metal Dichalcogenide ◽  
Pair Breaking ◽  
Electrical Insulator ◽  
Low Field ◽  
Vertical Electric Field ◽  
Half Filling

AbstractArtificial moiré superlattices in 2d van der Waals heterostructures are a new venue for realizing and controlling correlated electronic phenomena. Recently, twisted bilayer WSe2 emerged as a new robust moiré system hosting a correlated insulator at moiré half-filling over a range of twist angle. In this work, we present a theory of this insulating state as an excitonic density wave due to intervalley electron–hole pairing. We show that exciton condensation is strongly enhanced by a van Hove singularity near the Fermi level. Our theory explains the remarkable sensitivity of the insulating gap to the vertical electric field. In contrast, the gap is weakly reduced by a perpendicular magnetic field, with quadratic dependence at low field. The different responses to electric and magnetic field can be understood in terms of pair-breaking versus non-pair-breaking effects in a BCS analog of the system. We further predict superfluid spin transport in this electrical insulator, which can be detected by optical spin injection and spatial-temporal imaging.

scholarly journals Linear magnetoresistance in the low-field limit in density-wave materials

2019 ◽  
Vol 116 (23) ◽  
pp. 11201-11206 ◽  
Author(s):  
Yejun Feng ◽  
Yishu Wang ◽  
D. M. Silevitch ◽  
J.-Q. Yan ◽  
Riki Kobayashi ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Low Temperature ◽  
Applied Field ◽  
Density Wave ◽  
Spin Density Wave ◽  
Field Limit ◽  
Fermi Surfaces ◽  
Low Field ◽  
Metallic Charge ◽  
Linear Magnetoresistance

The magnetoresistance (MR) of a material is typically insensitive to reversing the applied field direction and varies quadratically with magnetic field in the low-field limit. Quantum effects, unusual topological band structures, and inhomogeneities that lead to wandering current paths can induce a cross-over from quadratic to linear MR with increasing magnetic field. Here we explore a series of metallic charge- and spin-density-wave systems that exhibit extremely large positive linear MR. By contrast to other linear MR mechanisms, this effect remains robust down to miniscule magnetic fields of tens of Oersted at low temperature. We frame an explanation of this phenomenon in a semiclassical narrative for a broad category of materials with partially gapped Fermi surfaces due to density waves.

High Magnetic Field Phases of the (TMTSF)2X (X = CLO4, PF6) Charge Transfer Complexes

1989 ◽  
Vol 173 ◽  
Author(s):  
J. S. Brooks ◽  
N. A. Fortune ◽  
P. M. Chaikin ◽  
L. Y. Chiang ◽  
G. Montambaux ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Charge Transfer ◽  
Magnetic Fields ◽  
Specific Heat ◽  
Low Temperatures ◽  
Density Wave ◽  
Spin Density Wave ◽  
Metallic State ◽  
Low Field ◽  
Fast Oscillations

ABSTRACTThe purpose of this talk is to discuss the physical properties of the (TMTSF)2X charge transfer salts in high magnetic fields. This class of materials is of great interest since the effective lower dimensionality and the various ground states are magnetic field dependent at low temperatures. At present, the so-called “standard model” provides a good theoretical description of the low field field induced spin density wave transitions (FISDW). However the reentrance from the last FISDW back to a high field metallic state, and the coexistence of “fast oscillations” in all measured properties, is yet to be accurately described theoretically. The emphasis of this paper is on recent specific heat results which have been obtained on (TMTSF)2ClO4 in magnetic fields as high as 30 T. Here we observe both the reentrant phase transition and the fast oscillations in the specific heat. A main conclusion we draw from our measurements is that the density of states in the reentrant phase is less than it is in the low field metallic state at low temperatures.

scholarly journals Topological gaps by twisting

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Matheus I. N. Rosa ◽  
Massimo Ruzzene ◽  
Emil Prodan
Keyword(s):  
Magnetic Field ◽  
Quantum Hall Effect ◽  
Twist Angle ◽  
Quantum Hall ◽  
Topological Phases ◽  
Edge States ◽  
Layered Systems ◽  
Virtual Laboratories ◽  
Higher Dimensional ◽  
Chern Numbers

AbstractTwisted bilayered systems such as bilayered graphene exhibit remarkable properties such as superconductivity at magic angles and topological insulating phases. For generic twist angles, the bilayers are truly quasiperiodic, a fact that is often overlooked and that has consequences which are largely unexplored. Herein, we uncover that twisted n-layers host intrinsic higher dimensional topological phases, and that those characterized by second Chern numbers can be found in twisted bi-layers. We employ phononic lattices with interactions modulated by a second twisted lattice and reveal Hofstadter-like spectral butterflies in terms of the twist angle, which acts as a pseudo magnetic field. The phason provided by the sliding of the layers lives on 2n-tori and can be used to access and manipulate the edge states. Our work demonstrates how multi-layered systems are virtual laboratories for studying the physics of higher dimensional quantum Hall effect, and can be employed to engineer topological pumps via simple twisting and sliding.

scholarly journals Experimental signatures of nodeless multiband superconductivity in a $$\hbox {2H-Pd}_{0.08} \hbox {TaSe}_2$$ single crystal

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Chanhee Kim ◽  
Dilip Bhoi ◽  
Yeahan Sur ◽  
Byung-Gu Jeon ◽  
Dirk Wulferding ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Single Crystal ◽  
Zero Magnetic Field ◽  
Anisotropy Ratio ◽  
Strong Temperature Dependence ◽  
Critical Fields ◽  
Band Theory ◽  
Plane Field ◽  
Low Field ◽  
Out Of Plane

AbstractIn order to understand the superconducting gap nature of a $$\hbox {2H-Pd}_{0.08} \hbox {TaSe}_2$$ 2H-Pd 0.08 TaSe 2 single crystal with $$T_{c} = 3.13 \text { K}$$ T c = 3.13 K , in-plane thermal conductivity $$\kappa $$ κ , in-plane London penetration depth $$\lambda _{\text {L}}$$ λ L , and the upper critical fields $$H_{c2}$$ H c 2 have been investigated. At zero magnetic field, it is found that no residual linear term $$\kappa _{0}/T$$ κ 0 / T exists and $$\lambda _{\text {L}}$$ λ L follows a power-law $$T^n$$ T n (T: temperature) with n = 2.66 at $$T \le \frac{1}{3}T_c$$ T ≤ 1 3 T c , supporting nodeless superconductivity. Moreover, the magnetic-field dependence of $$\kappa _{0}$$ κ 0 /T clearly shows a shoulder-like feature at a low field region. The temperature dependent $$H_{c2}$$ H c 2 curves for both in-plane and out-of-plane field directions exhibit clear upward curvatures near $$T_c$$ T c , consistent with the shape predicted by the two-band theory and the anisotropy ratio between the $$H_{c2}$$ H c 2 (T) curves exhibits strong temperature-dependence. All these results coherently suggest that $$\hbox {2H-Pd}_{0.08} \hbox {TaSe}_2$$ 2H-Pd 0.08 TaSe 2 is a nodeless, multiband superconductor.

scholarly journals Ground state and stability of the fractional plateau phase in metallic Shastry–Sutherland system TmB4

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Matúš Orendáč ◽  
Slavomír Gabáni ◽  
Pavol Farkašovský ◽  
Emil Gažo ◽  
Jozef Kačmarčík ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Phase Diagram ◽  
Ground State ◽  
Constant Magnetic Field ◽  
Paramagnetic Phase ◽  
The Other ◽  
Zero Field ◽  
Plateau Phase ◽  
Low Field ◽  
Zero Field Cooling

AbstractWe present a study of the ground state and stability of the fractional plateau phase (FPP) with M/Msat = 1/8 in the metallic Shastry–Sutherland system TmB4. Magnetization (M) measurements show that the FPP states are thermodynamically stable when the sample is cooled in constant magnetic field from the paramagnetic phase to the ordered one at 2 K. On the other hand, after zero-field cooling and subsequent magnetization these states appear to be of dynamic origin. In this case the FPP states are closely associated with the half plateau phase (HPP, M/Msat = ½), mediate the HPP to the low-field antiferromagnetic (AF) phase and depend on the thermodynamic history. Thus, in the same place of the phase diagram both, the stable and the metastable (dynamic) fractional plateau (FP) states, can be observed, depending on the way they are reached. In case of metastable FP states thermodynamic paths are identified that lead to very flat fractional plateaus in the FPP. Moreover, with a further decrease of magnetic field also the low-field AF phase becomes influenced and exhibits a plateau of the order of 1/1000 Msat.

scholarly journals Robust anomalous metallic states and vestiges of self-duality in two-dimensional granular In-InOx composites

2021 ◽  
Vol 6 (1) ◽  
Author(s):  
Xinyang Zhang ◽  
Bar Hen ◽  
Alexander Palevski ◽  
Aharon Kapitulnik
Keyword(s):  
Magnetic Field ◽  
Metallic Phase ◽  
Broadband Noise ◽  
Two Dimensional ◽  
Conventional Theory ◽  
Logarithmic Divergence ◽  
Self Duality ◽  
Low Field ◽  
Wide Range ◽  
Low Temperature Resistance

AbstractMany experiments investigating magnetic-field tuned superconductor-insulator transition (H-SIT) often exhibit low-temperature resistance saturation, which is interpreted as an anomalous metallic phase emerging from a ‘failed superconductor’, thus challenging conventional theory. Here we study a random granular array of indium islands grown on a gateable layer of indium-oxide. By tuning the intergrain couplings, we reveal a wide range of magnetic fields where resistance saturation is observed, under conditions of careful electromagnetic filtering and within a wide range of linear response. Exposure to external broadband noise or microwave radiation is shown to strengthen the tendency of superconductivity, where at low field a global superconducting phase is restored. Increasing magnetic field unveils an ‘avoided H-SIT’ that exhibits granularity-induced logarithmic divergence of the resistance/conductance above/below that transition, pointing to possible vestiges of the original emergent duality observed in a true H-SIT. We conclude that anomalous metallic phase is intimately associated with inherent inhomogeneities, exhibiting robust behavior at attainable temperatures for strongly granular two-dimensional systems.

scholarly journals Symmetry mediated tunable molecular magnetism on a 2D material

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Yuqi Wang ◽  
Soroush Arabi ◽  
Klaus Kern ◽  
Markus Ternes
Keyword(s):  
Single Molecule ◽  
Twist Angle ◽  
Layered Material ◽  
Spin Interaction ◽  
Transition Metal Dichalcogenide ◽  
Nanoscale Structures ◽  
Reduced Dimensions ◽  
Spin Interactions ◽  
Metal Organic ◽  
Probe Microscope

AbstractSymmetries in nanoscale structures can be decisive for their structural, electronic, and magnetic properties, particularly in systems with reduced dimensions. Here we show that the symmetries of a flat metal-organic molecule adsorbed on a transition metal dichalcogenide, a 2-dimensional layered material, have a dramatic effect on the total spin and the intramolecular spin-spin interactions. Using a scanning probe microscope, we find two different molecular spin states by modifying the symmetry of the molecules via the twist angle to the substrate. Additionally, we observe significant non-collinear Dzyaloshinskii–Moriya interaction between two electron spins on the molecule induced by the spin-orbit coupling of the van der Waals coupled layered material with broken inversion symmetry. Our work opens a path for modifying the spin by exploiting symmetries and for studying the nature of surface-induced non-collinear spin-spin interaction within a single molecule which might allow the realization of more complex topological spin structures.

Magnetic-field behavior of the spin-density-wave state in (TMTSF)2AsF6

1995 ◽  
Vol 52 (22) ◽  
pp. 15983-15991 ◽  
Author(s):  
J. L. Musfeldt ◽  
M. Poirier ◽  
P. Batail ◽  
C. Lenoir
Keyword(s):  
Magnetic Field ◽  
Spin Density ◽  
Density Wave ◽  
Spin Density Wave ◽  
Wave State ◽  
Field Behavior
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