Philip Kim

A15. 00004: Engineering Majorana bound states in coupled quantum dots in a two-dimensional electron gas

The interplay between strong correlation, magnetism, and band topology gives rise to various exciting quantum phenomena, including integer and fractional quantum anomalous Hall effects, charge density wave, unconventional superconductivity,… Recently, a new Uranium-based, van der Waals layered antiferromagnet with high Neel temperature (T N~ 150K), has been successfully synthesized and emerged as a promising intrinsic material platform to study such interplay due to the possible heavy fermionic nature and strong spin orbit coupling of Uranium. In this work, we present magneto-transport and magnetic circular dichroism studies in this Uranium-based antiferromagnet from bulk single crystal down to a few atomic layer thin flakes. Noticeably, despite its antiferromagnetic ground state, we observe finite anomalous Hall signal in thin flakes, which is absent in the bulk. The magnetic hysteresis loop …

W01. 00008: Corbino Josephson interferometry on a surface of topological insulator Sn-doped Bi 1.1 Sb 0.9 Te 2 S

Thermopower is a direct and sensitive probe of the entropy associated with charge carriers, including fractional quasiparticles, in a system. In particular, thermopower measurements on 2D electron gases, including both GaAs and graphene, have demonstrated quantized thermoelectric conductivity in the quantum hall (QH) regime, as predicted by Girvin and Jonson [1][2]. Attempts have also been made to measure even-denominator fractional QH states in GaAs, where theory predicts that the filling fraction dependence of thermopower can provide evidence for the possible non-Abelian nature of the ground state [3][4]. The weak electron-phonon coupling in graphene provides an advantage over GaAs by reducing the conflating effects of phonon drag to the thermopower measurements. We will discuss progress and challenges in thermopower measurements on high-quality, dual-encapsulated Bernal bilayer …

Imposing incommensurable periodicity on the periodic atomic lattice can lead to complex structural phases consisting of locally periodic structure bounded by topological defects. Twisted trilayer graphene (TTG) is an ideal material platform to study the interplay between different atomic periodicities, which can be tuned by twist angles between the layers, leading to moir\'e-of-moir\'e lattices. Interlayer and intralayer interactions between two interfaces in TTG transform this moir\'e-of-moir\'e lattice into an intricate network of domain structures at small twist angles, which can harbor exotic electronic behaviors. Here we report a complete structural phase diagram of TTG with atomic scale lattice reconstruction. Using transmission electron microscopy combined with a new interatomic potential simulation, we show that a cornucopia of large-scale moir\'e lattices, ranging from triangular, kagome, and a corner-shared hexagram-shaped domain pattern, are present. For small twist angles below 0.1{\deg}, all domains are bounded by a network of two-dimensional domain wall lattices. In particular, in the limit of small twist angles, the competition between interlayer stacking energy and the formation of discommensurate domain walls leads to unique spontaneous symmetry breaking structures with nematic orders, suggesting the pivotal role of long-range interactions across entire layers. The diverse tessellation of distinct domains, whose topological network can be tuned by the adjustment of the twist angles, establishes TTG as a platform for exploring the interplay between emerging quantum properties and controllable nontrivial lattices.

Atomically thin transition metal dichalcogenides (TMDs) are an exciting platform to study strongly correlated excitonic and electronic physics. However, electrical transport measurements in monolayer TMDs are limited by the ability to fabricate reliable electrodes, particularly n-type contacts to MoSe 2, MoS 2, and MoTe 2, due to Schottky barrier formation and metal-induced gap states. Efficient n-type contacts to these materials typically require work-function matching at the metal-semiconductor interface and heavy electron doping. Inspired by recent advances in p-type contacts to WSe 2 by RuCl 3 van der Waals ‘modulation’doping, we investigate interfacing TMDs with very low work-function metals to explore interfacial charge transfer. These efforts can be combined with an atomically clean monolayer hBN insertion barrier between the metal-semiconductor interface that has been demonstrated to lower the metal …

N47. 00014: Probing Kinetic Inductance in Thin Niobium Diselenide (NbSe 2) through Microwave Measurements*

Superfluid stiffness measurements offer a powerful probe of the superconducting state and a primary means to characterize their pairing symmetries. While penetration depth experiments can be used in bulk materials to extract superfluid stiffness, for two-dimensional materials with a small sample volume, alternative methods are required. Here we discuss the development of a technique to measure the superconducting kinetic inductance in low-dimensional materials and apply it to twisted multilayer graphene. We investigate superfluid stiffness as a function of carrier density and temperature and provide interpretations for possible pairing symmetries.

Employing flux-grown single crystal WSe 2, we report charge-carrier scattering behaviors measured in h-BN encapsulated monolayer field effect transistors. We observe a nonmonotonic change of transport mobility as a function of hole density in the degenerately doped sample, which can be explained by energy dependent scattering amplitude of strong defects calculated using the T-matrix approximation. Utilizing long mean-free path (> 500 nm), we also demonstrate the high quality of our electronic devices by showing quantized conductance steps from an electrostatically defined quantum point contact, showing the potential for creating ultrahigh quality quantum optoelectronic devices based on atomically thin semiconductors.

F09. 00002: Second-order correlation measurements of electrically generated interlayer excitons in atomically thin semiconductor heterostructures

The recent discovery of interaction-driven viscous electronic hydrodynamics in graphene has inspired new devices and insights about other materials. In this new regime, the well-known rules of Ohmic transport no longer apply, and a number of effects have been identified in electronic transport. Despite these advancements, the hydrodynamic analogue of Joule heating remains unexplored, and the thermal properties of hydrodynamic electronic devices are unknown. In this work, we probe graphene hydrodynamics with thermal transport and find two distinct, qualitative signatures: thermal conductivity suppression below the Wiedemann-Franz value and negative thermal magnetoresistance. These signatures arise from two distinct aspects of this new regime: microscopic momentum conservation due to electron-electron scattering, and geometry-dependent viscous dissipation. We find they are coincident in …

W07. 00010: Magnetoresistance and Hall Resistance Hysteresis in the 2D Heavy Fermion Antiferromagnet CeSiI*

(57) ABSTRACT A semiconductor device includes a substrate, a two-dimen sional (2D) material layer formed on the substrate and having a first region and a second region adjacent to the first region, and a source electrode and a drain electrode provided to be respectively in contact with the first region and the second region of the 2D material layer, the second region of the 2D material layer including an oxygen adsorption mate rial layer in which oxygen is adsorbed on a surface of the second region. 17 Claims, 17 Drawing Sheets

Disorder at the etched edges of graphene quantum dots (GQD) enables random all-to-all interactions between localized charges in partially-filled Landau levels, providing a potential platform to realize the Sachdev-Ye-Kitaev (SYK) model. We use quantum Hall edge states in the graphene electrodes to measure electrical conductance and thermoelectric power across the GQD. We observe a rapid diminishing of electric conductance fluctuations and slowly decreasing thermoelectric power across the GQD with increasing temperature, consistent with recent theoretical predictions for the SYK regime.

F17. 00002: Strongly coupled edge states and frequency doubling in a graphene quantum Hall interferometer

Insulators do not carry DC current but can conduct electricity at high frequencies. In a quantum Hall insulator, this capacitive current is enabled by the time-dependent polarization of Landau orbits and is expected to carry information about the quantum geometry of the underlying Hilbert space. To measure this conductance, we embed a graphene quantum Hall insulator in a resonator where a dispersive shift of the resonator frequency sensitively tracks the capacitive response of these insulating states. Finite temperature and disorder broadening creates a conventional quantum capacitive response that competes with the quantum geometric contribution. We discuss ways to disentangle these contributions and show preliminary experiments.

The twisted interface of van der Waals (vdW) materials provides a new platform where exotic new material properties emerge. One of the most recent discoveries is the appearance of ferroelectric domains in twisted stacked vdW layers with engineered non-centrosymmetry. While various local probes and global transport measurements reveal the ferroelectric domains with alternating dipole moments formed in the moiré lattice, the nature of the domain dynamics in relation to the ferroelectric hysteresis and its connection to the atomic and moiré structure remains a mystery. In this talk, we discuss a framework for understanding the polar domain dynamics in the moiré superlattice. We show the moiré domains with alternating dipole moments as an unconventional polar state of a domain antiferroelectric (DAF) with the characteristic topology of a domain wall network (DWN) configuration. Monitoring the structural change …

The search for anyons, quasiparticles with fractional charge and exotic exchange statistics, has inspired decades of condensed matter research. Quantum Hall interferometers enable direct observation of the anyon braiding phase via discrete interference phase jumps when the quasiparticle number changes. Here, we observe the universal anyonic braiding phase in both the and fractional quantum Hall states by probing three-state random telegraph noise (RTN) in real-time. We find that the observed RTN stems from anyon quasiparticle number fluctuations and reconstruct three Aharonov-Bohm oscillation signals phase shifted by , corresponding to the three possible interference branches from braiding around (mod 3) anyons. Hence, we fully characterize the anyon exchange statistics using new methods that can readily extend to non-abelian states.

Heavy-fermion metals are prototype systems for observing emergent quantum phases driven by electronic interactions 1, 2, 3, 4, 5, 6. A long-standing aspiration is the dimensional reduction of these materials to exert control over their quantum phases 7, 8, 9, 10, 11, which remains a significant challenge because traditional intermetallic heavy-fermion compounds have three-dimensional atomic and electronic structures. Here we report comprehensive thermodynamic and spectroscopic evidence of an antiferromagnetically ordered heavy-fermion ground state in CeSiI, an intermetallic comprising two-dimensional (2D) metallic sheets held together by weak interlayer van der Waals (vdW) interactions. Owing to its vdW nature, CeSiI has a quasi-2D electronic structure, and we can control its physical dimension through exfoliation. The emergence of coherent hybridization of f and conduction electrons at low temperature …

Correlation-driven stripe charge order in doped antiferromagnets has been proposed as a crucial concept in understanding the mechanism of high-temperature superconductors. In a newly emerged van der Waals antiferromagnet U-base tellurides, we discovered a robust stripe charge density wave (CDW) phase that persists above room temperature. Scanning tunneling microscopy and spectroscopy reveal “flat bands” near the Fermi level, indicating strong electron correlation in this system. Electron microscopy demonstrates the presence of coherent CDW and CDW domains on a macroscopic scale. This CDW manifests as significant anisotropic transport behavior over a wide range of temperatures, suggesting potential future device applications. Our study establishes this new U-based telluride as a promising platform for investigating the interplay between electron correlation, stripe charge order, and magnetism.