arXiv subjects

Tanmay Maiti

Publications and source records attributed to Tanmay Maiti.

10 recordsLinked to original sources

arXiv2026

Emergent Chiral Metal Phase in Compressible Quantum Hall Fluids

We report transmitted conductance measurements between a source and reflection-less contacts connected to a compressible quantum Hall fluid with filling fraction $\nu$. We observe that total sum of transmitted conductances universally approaches Hall conductance $\nu(e^2/h)$. The universality of this sum rule is established experimentally across integer and fractional quantum Hall regimes, remaining invariant under variation in temperatures, sample geometries, material qualities and quasi-particle interactions. Chiral transport in compressible quantum Hall fluids, characterized by suppressed dissipative transport with a distinct handedness, is confirmed by floating contact measurements. Consequently, this sum rule emerges as a conduction law of the chiral metal phase. Theoretically, we argue that time-reversal-symmetry breaking under a strong magnetic field within this chiral metal gives rise unidirectional trajectories of carriers in a nearly flat potential landscape with point-like disorder potentials, a regime realized when the screening length is smaller than the magnetic length. Within this chiral framework, longitudinal resistance does not originate from bulk dissipation but primarily from the equilibration of electrochemical potentials at the contacts. Our study introduces a new paradigm of chiral transport across a broad class of gapless two-dimensional systems characterized by short-range screening and broken time-reversal symmetry.

cond-mat.mes-hall↗

arXiv2025

Topological Robustness of Anyon Tunneling at $\nu = 1/3$

The scaling exponent $g$ of the quasiparticle propagator for incompressible fractional quantum Hall states in the Laughlin sequence is expected to be robust against perturbations that do not close the gap. Here we probe the topological robustness of the chiral Luttinger liquid at the boundary of the $\nu=1/3$ state by measuring the tunneling conductance between counterpropagating edge modes as a function of quantum point contact transmission. We demonstrate that for transmission $t\geq 0.7$ the tunneling conductance is well-described by the first two terms of a perturbative series expansion corresponding to $g=1/3$. We further demonstrate that the measured scaling exponent is robustly pinned to $g=1/3$ across the plateau, only deviating as the bulk state becomes compressible. Finally we examine the impact of weak disorder on the scaling exponent, finding it insensitive. These measurements firmly establish the topological robustness of anyon tunneling at $\nu=1/3$ and substantiate the chiral Luttinger liquid description of the edge mode.

cond-mat.mes-hall↗

arXiv2025

Collapse of edge reconstruction in compressible Quantum Hall fluid within filling fraction range 2/3 to 1

The edge structure of a gate-defined compressible quantum Hall fluids in the filling fraction range 2/3 to 1 is studied using the three reconstructed $e^2/3h$ fractional edge modes of unity filling integer quantum Hall state. We find that the individually excited partially resolved $e^2/3h$ edge modes of the bulk state equilibrate completely even at higher magnetic field when passing through the gate defined compressible fluid with filling between 2/3 and 1. This result is unexpected because edge reconstruction at the smooth boundary is generally expected due to dominant incompressibility at filling 2/3 and 1/3. Recently such reconstructed edge mode has been reported for the compressible fluid in the filling fraction range 1/3 to 2/3. In contrary, equilibration of fractional edge modes in the compressible fluid within the filling fraction range 2/3 to 1 becomes faster with increasing magnetic field. This anomalous results will stimulate further investigations on edge structure in these complex many body systems.

cond-mat.mes-hall↗

arXiv2025

Universal Anyon Tunneling in a Chiral Luttinger Liquid

The edge modes of fractional quantum Hall liquids are described by chiral Luttinger liquid theory. Despite many years of experimental investigation fractional quantum Hall edge modes remain enigmatic with significant discrepancies between experimental observations and detailed predictions of chiral Luttinger liquid theory. Here we report measurements of tunneling conductance between counterpropagating edge modes at $\nu=1/3$ across a quantum point contact fabricated on an AlGaAs/GaAs heterostructure designed to promote a sharp confinement potential. We present evidence for tunneling of anyons through a $\nu=1/3$ incompressible liquid that exhibits universal scaling behavior with respect to temperature, source-drain bias, and barrier transmission, as originally proposed by Wen [1, 2]. For transmission $t\geq0.800$, we measured the tunneling exponent $\bar{g} = 0.333 \pm 0.005$ averaged over 29 independent data sets, consistent with the scaling dimension $\Delta = g/2 = 1/6$ for a Laughlin quasiparticle at the edge. When combined with measurements of the fractional charge $e^*=e/3$ and the recently observed anyonic statistical angle $\theta_a=\frac{2\pi}{3}$, the measured tunneling exponent fully characterizes the topological order of the primary Laughlin state at $\nu=1/3$.

cond-mat.mes-hall↗

arXiv2024

Edge reconstruction of compressible Quantum Hall fluid in the filling fraction range 1/3 to 2/3

Edge reconstruction of gate-tunable compressible quantum Hall fluids in the filling fraction range 1/3 to 2/3 is studied by measuring transmitted conductance of two individually excited fractional $e^2/3h$ edge modes of bulk 2/3 fractional quantum Hall fluid. Our findings reveal that the measured transmitted conductance deviates from the fully equilibrated value for the filling fraction range 1/3 to 2/3 of the gate-tunable compressible quantum Hall fluids at higher magnetic fields. This observation suggests that at the boundary of the compressible fluid a reconstructed $e^2/3h$ fractional edge mode is present and the mode does not completely equilibrate with the inner dissipative bulk region. Consequently, this outer reconstructed edge mode supports adiabatic charge transport, allowing non-equilibrated current transport through the compressible region. These studies open new avenues for achieving robust fractional edge modes even in compressible quantum Hall fluids under strong magnetic fields, enhancing our understanding of edge state dynamics in these complex systems.

cond-mat.mes-hall↗

arXiv2024

Optimization of submicron Ni/Au/Ge contacts to an AlGaAs/GaAs two-dimensional electron gas

We report on fabrication and performance of submicron Ni/Au/Ge contacts to a two-dimensional electron gas in an AlGaAs/GaAs heterostructure. Utilizing scanning transmission electron microscopy, energy dispersive x-ray spectroscopy, and low temperature electrical measurements we investigate the relationship between contact performance and the mechanical and chemical properties of the annealed metal stack. Contact geometry and crystallographic orientation significantly impact performance. Our results indicate that the spatial distribution of germanium in the annealed contact plays a central role in the creation of high transmission contacts. We characterize the transmission of our contacts at high magnetic fields in the quantum Hall regime. Our work establishes that contacts with area 0.5 square microns and resistance less than 400 Ohms can be fabricated with high yield.

cond-mat.mes-hall↗

arXiv2022

Formation of tungsten carbide by focused ion beam process: A route to high magnetic field resilient patterned superconducting nanostructures

A scale for magnetic field resilience of a superconductor is set by the paramagnetic limit. Comparing the condensation energy of the Bardeen-Cooper-Schrieffer (BCS) singlet ground state with the paramagnetically polarised state suggests that for an applied field ${μ_0}H > 1.8~T_c$ (in SI), singlet pairing is not energetically favourable. Materials exceeding or approaching this limit are interesting from fundamental and technological perspectives. This may be a potential indicator of triplet superconductivity, Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) pairing and other mechanisms involving topological aspects of surface states, and also allow Cooper pair injection at high magnetic fields. We have analysed the microscopic composition of such a material arising from an unexpected source. A microjet of an organo-metallic gas, $\rm {W[(CO)_6]}$ can be decomposed by gallium ion-beam, leaving behind a track of complex residue of gallium, tungsten and carbon with remarkable superconducting properties, like an upper critical field, $H_{c2} > 10~{\rm T} $, above its paramagnetic limit. We carried out Atomic probe tomography to establish the formation of nano-crystalline tungsten carbide (WC) in the tracks and the absence of free tungsten. Supporting calculations show for Ga distributed on the surface of WC, its s,p-orbitals enhance the density of states near the Fermi energy. The observed variation of $H_{c2}(T)$ does not show features typical of enhancement of critical field due to granularity. Our observations may be significant in the context of some recent theoretical calculation of the band structure of WC and experimental observation of superconductivity in WC-metal interface.

cond-mat.supr-con↗

arXiv2021

Superconductivity coexisting with ferromagnetism in a quasi-one dimensional non-centrosymmetric (TaSe$_4$)$_3$I

Low-dimensional materials with broken inversion symmetry and strong spin-orbit coupling can give rise to fascinating quantum phases and phase transitions. Here we report coexistence of superconductivity and ferromagnetism below 2.5\,K in the quasi-one dimensional crystals of non-centrosymmetric (TaSe$_4$)$_3$I (space group: $P\bar{4}2_1c$). The unique phase is a direct consequence of inversion symmetry breaking as the same material also stabilizes in a centro-symmetric structure (space group: $P4/mnc$) where it behaves like a non-magnetic insulator. The coexistence here upfront contradicts the popular belief that superconductivity and ferromagnetism are two apparently antagonistic phenomena. Notably, here, for the first time, we have clearly detected Meissner effect in the superconducting state despite the coexisting ferromagnetic order. The coexistence of superconductivity and ferromagnetism projects non-centrosymmetric (TaSe$_4$)$_3$I as a host for complex ground states of quantum matter including possible unconventional superconductivity with elusive spin-triplet pairing.

cond-mat.supr-con↗

arXiv2021

Temperature dependent equilibration of spin orthogonal quantum Hall edge modes

Conductance of the edge modes as well as conductance across the co-propagating edge modes around the ν= 4/3, 5/3 and 2 quantum Hall states are measured by individually exciting the modes. Temperature dependent equilibration rates of the outer unity conductance edge mode are presented for different filling fractions. We find that the equilibration rate of the outer unity conductance mode at ν= 2 is higher and more temperature sensitive compared to the mode at fractional filling 5/3 and 4/3. At lowest temperature, equilibration length of the outer unity conductance mode tends to saturate with lowering filling fraction νby increasing magnetic field B. We speculate this saturating nature of equilibration length is arising from an interplay of Coulomb correlation and spin orthogonality.

cond-mat.mes-hall↗

arXiv2020

Magnetic field dependent equilibration of fractional quantum Hall edge modes

Fractional conductance is measured by partitioning $ν= 1$ edge state using gate-tunable fractional quantum Hall (FQH) liquids of filling 1/3 or 2/3 for current injection and detection. We observe two sets of FQH plateaus 1/9, 2/9, 4/9 and 1/6, 1/3, 2/3 at low and high magnetic field ends of the $ν= 1$ plateau respectively. The findings are explained by magnetic field dependent equilibration of three FQH edge modes with conductance $e^2/3h$ arising from edge reconstruction. The results reveal remarkable enhancement of the equilibration lengths of the FQH edge modes with increasing field.

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