Publications by authors named "Abhay N Pasupathy"

Article Synopsis
  • Noncentrosymmetric two-dimensional superconductors like few-layer T_{d}-MoTe_{2} exhibit unique superconducting properties, including upper critical fields exceeding the Pauli limit by up to 600%.
  • The enhancement of these properties is still debated, with theories suggesting influences from either spin-orbit parity coupling or tilted Ising spin-orbit coupling.
  • In bilayer T_{d}-MoTe_{2}, experiments show superconductivity has a twofold symmetry influenced by magnetic and electric fields, and findings support tilted Ising spin-orbit coupling as the main mechanism.
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Ultraclean graphene at charge neutrality hosts a quantum critical Dirac fluid of interacting electrons and holes. Interactions profoundly affect the charge dynamics of graphene, which is encoded in the properties of its electron-photon collective modes: surface plasmon polaritons (SPPs). Here, we show that polaritonic interference patterns are particularly well suited to unveil the interactions in Dirac fluids by tracking polaritonic interference in time at temporal scales commensurate with the electronic scattering.

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Kagome vanadates AVSb display unusual low-temperature electronic properties including charge density waves (CDW), whose microscopic origin remains unsettled. Recently, CDW order has been discovered in a new material ScVSn, providing an opportunity to explore whether the onset of CDW leads to unusual electronic properties. Here, we study this question using angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM).

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Highly tunable properties make Mn(Bi,Sb)Te a rich playground for exploring the interplay between band topology and magnetism: On one end, MnBiTe is an antiferromagnetic topological insulator, while the magnetic structure of MnSbTe (MST) can be tuned between antiferromagnetic and ferrimagnetic. Motivated to control electronic properties through real-space magnetic textures, we use magnetic force microscopy (MFM) to image the domains of ferrimagnetic MST. We find that magnetic field tunes between stripe and bubble domain morphologies, raising the possibility of topological spin textures.

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The integration time and signal-to-noise ratio are inextricably linked when performing scanning probe microscopy based on raster scanning. This often yields a large lower bound on the measurement time, for example, in nano-optical imaging experiments performed using a scanning near-field optical microscope (SNOM). Here, we utilize sparse scanning augmented with Gaussian process regression to bypass the time constraint.

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Since the seminal work on MoS, photoexcitation in atomically thin transition metal dichalcogenides (TMDCs) has been assumed to result in excitons, with binding energies order of magnitude larger than thermal energy at room temperature. Here, we reexamine this foundational assumption and show that photoexcitation of TMDC monolayers can result in a substantial population of free charges. Performing ultrafast terahertz spectroscopy on large-area, single-crystal TMDC monolayers, we find that up to ~10% of excitons spontaneously dissociate into charge carriers with lifetimes exceeding 0.

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Heavy-fermion metals are prototype systems for observing emergent quantum phases driven by electronic interactions. A long-standing aspiration is the dimensional reduction of these materials to exert control over their quantum phases, 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.

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Defects significantly affect the electronic, chemical, mechanical, and optical properties of two-dimensional (2D) materials. Thus, it is critical to develop a method for convenient and reliable defect quantification. Scanning transmission electron microscopy (STEM) and scanning tunneling microscopy (STM) possess the required atomic resolution but have practical disadvantages.

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Forming a hetero-interface is a materials-design strategy that can access an astronomically large phase space. However, the immense phase space necessitates a high-throughput approach for an optimal interface design. Here we introduce a high-throughput computational framework, InterMatch, for efficiently predicting charge transfer, strain, and superlattice structure of an interface by leveraging the databases of individual bulk materials.

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Two-dimensional antiferromagnets have garnered considerable interest for the next generation of functional spintronics. However, many bulk materials from which two-dimensional antiferromagnets are isolated are limited by their air sensitivity, low ordering temperatures, and insulating transport properties. TaFeTe aims to address these challenges with increased air stability, metallic transport, and robust antiferromagnetism.

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Two-dimensional transition-metal dichalcogenides (TMDs) have attracted tremendous interest due to the unusual electronic and optoelectronic properties of isolated monolayers and the ability to assemble diverse monolayers into complex heterostructures. To understand the intrinsic properties of TMDs and fully realize their potential in applications and fundamental studies, high-purity materials are required. Here, we describe the synthesis of TMD crystals using a two-step flux growth method that eliminates a major potential source of contamination.

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Modern scanning probe techniques, such as scanning tunneling microscopy, provide access to a large amount of data encoding the underlying physics of quantum matter. In this work, we show how convolutional neural networks can be used to learn effective theoretical models from scanning tunneling microscopy data on correlated moiré superlattices. Moiré systems are particularly well suited for this task as their increased lattice constant provides access to intra-unit-cell physics, while their tunability allows for the collection of high-dimensional data sets from a single sample.

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As one of the most fundamental physical phenomena, charge density wave (CDW) order predominantly occurs in metallic systems such as quasi-1D metals, doped cuprates, and transition metal dichalcogenides, where it is well understood in terms of Fermi surface nesting and electron-phonon coupling mechanisms. On the other hand, CDW phenomena in semiconducting systems, particularly at the low carrier concentration limit, are less common and feature intricate characteristics, which often necessitate the exploration of novel mechanisms, such as electron-hole coupling or Mott physics, to explain. In this study, an approach combining electrical transport, synchrotron X-ray diffraction, and density-functional theory calculations is used to investigate CDW order and a series of hysteretic phase transitions in a dilute d-band semiconductor, BaTiS .

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Article Synopsis
  • The study explores the use of work-function-mediated charge transfer for controlling the electrostatics of individual atomic layers, using α-RuCl as a 2D electron acceptor next to hexagonal boron nitride (BN).
  • It highlights how this arrangement induces unique nano-optical behavior in BN by causing interlayer charge polarization, resulting in a reduction of phonon polariton (PhP) propagation length significantly beyond intrinsic losses.
  • The findings are backed by advanced techniques like scattering-type scanning near-field optical microscopy and first-principles calculations, demonstrating the promising applications of charge-transfer heterostructures in enhancing the optoelectronic properties of 2D insulators.
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The pair density wave (PDW) is a superconducting state in which Cooper pairs carry centre-of-mass momentum in equilibrium, leading to the breaking of translational symmetry. Experimental evidence for such a state exists in high magnetic field and in some materials that feature density-wave orders that explicitly break translational symmetry. However, evidence for a zero-field PDW state that exists independent of other spatially ordered states has so far been elusive.

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We investigate heterostructures composed of monolayer WSe stacked on α-RuCl using a combination of Terahertz (THz) and infrared (IR) nanospectroscopy and imaging, scanning tunneling spectroscopy (STS), and photoluminescence (PL). Our observations reveal itinerant carriers in the heterostructure prompted by charge transfer across the WSe/α-RuCl interface. Local STS measurements show the Fermi level is shifted to the valence band edge of WSe which is consistent with p-type doping and verified by density functional theory (DFT) calculations.

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Achieving electrostatic control of quantum phases is at the frontier of condensed matter research. Recent investigations have revealed superconductivity tunable by electrostatic doping in twisted graphene heterostructures and in two-dimensional semimetals such as WTe (refs. ).

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The electronic and structural properties of atomically thin materials can be controllably tuned by assembling them with an interlayer twist. During this process, constituent layers spontaneously rearrange themselves in search of a lowest energy configuration. Such relaxation phenomena can lead to unexpected and novel material properties.

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The ability to perform nanometer-scale optical imaging and spectroscopy is key to deciphering the low-energy effects in quantum materials, as well as vibrational fingerprints in planetary and extraterrestrial particles, catalytic substances, and aqueous biological samples. These tasks can be accomplished by the scattering-type scanning near-field optical microscopy (s-SNOM) technique that has recently spread to many research fields and enabled notable discoveries. Herein, it is shown that the s-SNOM, together with scanning probe research in general, can benefit in many ways from artificial-intelligence (AI) and machine-learning (ML) algorithms.

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The optical properties of transition-metal dichalcogenides have previously been modified at the nanoscale by using mechanical and electrical nanostructuring. However, a clear experimental picture relating the local electronic structure with emission properties in such structures has so far been lacking. Here, we use a combination of scanning tunneling microscopy (STM) and near-field photoluminescence (nano-PL) to probe the electronic and optical properties of single nanobubbles in bilayer heterostructures of WSe on MoSe.

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CaRuO is a transition-metal oxide that exhibits a Mott insulator-metal transition (IMT) concurrent with a symmetry-preserving Jahn-Teller distortion (JT) at 350 K. The coincidence of these two transitions demonstrates a high level of coupling between the electronic and structural degrees of freedom in CaRuO. Using spectroscopic measurements with nanoscale spatial resolution, we interrogate the interplay of the JT and IMT through the temperature-driven transition.

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Semiconductors, featuring tunable electrical transport, and magnets, featuring tunable spin configurations, form the basis of many information technologies. A long-standing challenge has been to realize materials that integrate and connect these two distinct properties. Two-dimensional (2D) materials offer a platform to realize this concept, but known 2D magnetic semiconductors are electrically insulating in their magnetic phase.

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2D materials can host long-range magnetic order in the presence of underlying magnetic anisotropy. The ability to realize the full potential of 2D magnets necessitates systematic investigation of the role of individual atomic layers and nanoscale inhomogeneity (i.e.

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Magic-angle twisted trilayer graphene (TTG) has recently emerged as a platform to engineer strongly correlated flat bands. We reveal the normal-state structural and electronic properties of TTG using low-temperature scanning tunneling microscopy at twist angles for which superconductivity has been observed. Real trilayer samples undergo a strong reconstruction of the moiré lattice, which locks layers into near-magic-angle, mirror symmetric domains comparable in size with the superconducting coherence length.

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