arXiv subjects

Saumya Mukherjee

Publications and source records attributed to Saumya Mukherjee.

9 recordsLinked to original sources

arXiv2025

Anatomy of anomalous Hall effect due to magnetic fluctuations

The anomalous Hall {\color{black} e}ffect (AHE) has emerged as a key indicator of time-reversal symmetry breaking (TRSB) and topological features in electronic band structures. Absent of a magnetic field, the AHE requires spontaneous TRSB but has proven hard to probe due to averaging over domains. The anomalous component of the Hall effect is thus frequently derived from extrapolating the magnetic field dependence of the Hall response. We show that discerning whether the AHE is an intrinsic property of the field free system becomes intricate in the presence of strong magnetic fluctuations. {\color{black}As a study case,} we use the Weyl semimetal PrAlGe, where TRSB can be toggled via a ferromagnetic transition, providing a transparent view of the AHE's topological origin. Through a combination of thermodynamic, transport and muon spin relaxation measurements, we contrast the behaviour below the ferromagnetic transition temperature to that of strong magnetic fluctuations above. Our results {\color{black}on PrAlGe provide general insights into the} interpretation of anomalous Hall signals in systems where TRSB is debated, such as families of Kagome metals or certain transition metal dichalcogenides.

cond-mat.str-el↗

arXiv2024

Holstein polarons, Rashba-like spin splitting and Ising superconductivity in electron-doped MoSe2

Interaction between electrons and phonons in solids is a key effect defining physical properties of materials such as electrical and thermal conductivity. In transitional metal dichalcogenides (TMDCs) the electron-phonon coupling results in the creation of polarons, quasiparticles that manifest themselves as discrete features in the electronic spectral function. In this study, we report the formation of polarons at the alkali dosed MoSe2 surface, where Rashba-like spin splitting of the conduction band states is caused by an inversion-symmetry breaking electric field. In addition, we observe the crossover from phonon-like to plasmon-like polaronic spectral features at MoSe2 surface with increasing doping. Our findings support the concept of electron-phonon coupling mediated superconductivity in electron-doped layered TMDC materials, observed using ionic liquid gating technology. Furthermore, the discovered spin-splitting at the Fermi level could offer crucial experimental validation for theoretical models of Ising-type superconductivity in these materials.

cond-mat.supr-con↗

arXiv2020

Coexistence of type-I and type-II superconductivity signatures in ZrB12 probed by muon spin rotation measurements

Superconductors usually display either type-I or type-II superconductivity and the coexistence of these two types in the same material, for example at different temperatures is rare in nature. We the employed muon spin rotation (muSR) technique to unveil the superconducting phase diagram of the dodecaboride ZrB12 and obtained clear evidence of both type-I and type-II characteristics. Most importantly, we found a region showing unusual behavior where the usually mutually exclusive muSR signatures of type-I and type-II superconductivity coexist. We reproduced that behavior in theoretical modeling that required taking into account multiple bands and multiple coherence lengths, which suggests that material has one coherence length larger and another smaller than the magnetic field penetration length (the type-1.5 regime). At stronger fields, a footprint of the type-II mixed state showing square flux-line lattice was also obtained using neutron diffraction.

cond-mat.supr-con↗

arXiv2020

Spectral functions of CVD grown MoS$_2$ monolayers after chemical transfer onto Au surface

The recent rise of van der Waals (vdW) crystals has opened new prospects for studying versatile and exotic fundamental physics with future device applications such as twistronics. Even though the recent development on Angle-resolved photoemission spectroscopy (ARPES) with Nano-focusing optics, making clean surfaces and interfaces of chemically transferred crystals have been challenging to obtain high-resolution ARPES spectra. Here, we show that by employing nano-ARPES with submicron sized beam and polystyrene-assisted transfer followed by annealing process in ultra-high vacuum environment, remarkably clear ARPES spectral features such as spin-orbit splitting and band renormalization of CVD-grown, monolayered MoS2 can be measured. Our finding paves a way to exploit chemically transferred crystals for measuring high-resolution ARPES spectra to observe exotic quasi-particles in vdW heterostructures.

cond-mat.mes-hall↗

arXiv2020

Bulk and surface electronic states in the dosed semimetallic HfTe$\boldsymbol{_2}$

The dosing of layered materials with alkali metals has become a commonly used strategy in ARPES experiments. However, precisely what occurs under such conditions, both structurally and electronically, has remained a matter of debate. Here we perform a systematic study of 1T-HfTe$_2$, a prototypical semimetal of the transition metal dichalcogenide family. By utilizing photon energy-dependent angle-resolved photoemission spectroscopy (ARPES), we have investigated the electronic structure of this material as a function of Potassium (K) deposition. From the k$_z$ maps, we observe the appearance of 2D dispersive bands after electron dosing, with an increasing sharpness of the bands, consistent with the wavefunction confinement at the topmost layer. In our highest-dosing cases, a monolayer-like electronic structure emerges, presumably as a result of intercalation of the alkali metal. Here, by bringing the topmost valence band below $E_F$, we can directly measure a band overlap of $\sim$ 0.2 eV. However, 3D bulk-like states still contribute to the spectra even after considerable dosing. Our work provides a reference point for the increasingly popular studies of the alkali metal dosing of semimetals using ARPES.

cond-mat.mtrl-sci↗

arXiv2019

Direct observation of the energy gain underpinning ferromagnetic superexchange in the electronic structure of CrGeTe$_3$

We investigate the temperature-dependent electronic structure of the van der Waals ferromagnet, CrGeTe$_3$. Using angle-resolved photoemission spectroscopy, we identify atomic- and orbital-specific band shifts upon cooling through ${T_\mathrm{C}}$. From these, together with x-ray absorption spectroscopy and x-ray magnetic circular dichroism measurements, we identify the states created by a covalent bond between the Te ${5p}$ and the Cr ${e_g}$ orbitals as the primary driver of the ferromagnetic ordering in this system, while it is the Cr ${t_{2g}}$ states that carry the majority of the spin moment. The ${t_{2g}}$ states furthermore exhibit a marked bandwidth increase and a remarkable lifetime enhancement upon entering the ordered phase, pointing to a delicate interplay between localized and itinerant states in this family of layered ferromagnets.

cond-mat.str-el↗

arXiv2019

Fermi-crossing Type-II Dirac fermions and topological surface states in NiTe2

Transition-metal dichalcogenides (TMDs) offer an ideal platform to experimentally realize Dirac fermions. However, typically these exotic quasiparticles are located far away from the Fermi level, limiting the contribution of Dirac-like carriers to the transport properties. Here we show that NiTe2 hosts both bulk Type-II Dirac points and topological surface states. The underlying mechanism is shared with other TMDs and based on the generic topological character of the Te p-orbital manifold. However, unique to NiTe2, a significant contribution of Ni d orbital states shifts the energy of the Type-II Dirac point close to the Fermi level. In addition, one of the topological surface states intersects the Fermi energy and exhibits a remarkably large spin splitting of 120 meV. Our results establish NiTe2 as an exciting candidate for next-generation spintronics devices.

cond-mat.mtrl-sci↗

arXiv2017

Single-axis dependent structural and multiferroic properties of orthorhombic RMnO$_3$ (R = Gd - Lu)

Controlling material properties by modulating the crystalline structure has been attempted using various techniques, e.g., hydrostatic pressure, chemical pressure, and epitaxy. These techniques succeed to improve properties and achieve desired functionalities by changing the unit cell in all dimensions. In order to obtain a more detailed understanding on the relation between the crystal lattice and material properties, it is desirable to investigate the influence of a smaller number of parameters. Here, we utilize the combination of chemical pressure and epitaxy to modify a single lattice parameter of the multiferroic orthorhombic RMnO$_3$ (R = rare-earth, o-RMnO$_3$) system. By growing a series of o-RMnO$_3$ (R = Gd - Lu) films coherently on (010)-oriented YAlO$_3$ substrates, the influence of chemical pressure is reflected only along the $b$-axis. Thus, a series of o-RMnO$_3$ with $a$ ~ 5.18 Å, 5.77 Å < $b$ < 5.98 Å, and $c$ ~ 7.37 Å were obtained. Raman spectra analysis reveals that the change of the $b$-axis parameter induces a shift of the oxygen in the nominally "fixed" $ca$-plane. Their ferroelectric ground state is independent on the $b$-axis parameter showing polarization of ~ 1 $μ$C cm$^{-2}$ along the $a$-axis for the above-mentioned range, except for $b$ ~ 5.94 Å which corresponds to TbMnO$_3$ showing ~ 2 $μ$C cm$^{-2}$. This result implies that multiferroic order of o-RMnO$_3$ is almost robust against the $b$-axis parameter provided that the dimension of the $ca$-plane is fixed to 7.37 Å $\times$ 5.18 Å.

cond-mat.mtrl-sci↗

arXiv2017

Tuning the multiferroic mechanisms of TbMnO3 by epitaxial strain

A current challenge in the field of magnetoelectric multiferroics is to identify systems that allow a controlled tuning of states displaying distinct magnetoelectric responses. Here we show that the multiferroic ground state of the archetypal multiferroic TbMnO3 is dramatically modified by epitaxial strain. Neutron diffraction reveals that in highly strained films the magnetic order changes from the bulk-like incommensurate bc-cycloidal structure to commensurate magnetic order. Concomitant with the modification of the magnetic ground state, optical second-harmonic generation (SHG) and electric measurements show an enormous increase of the ferroelectric polarization, and a change in its direction from along the c- to the a-axis. Our results suggest that the drastic change of multiferroic properties results from a switch of the spin-current magnetoelectric coupling in bulk TbMnO3 to symmetric magnetostriction in epitaxially-strained TbMnO3. These findings experimentally demonstrate that epitaxial strain can be used to control single-phase spin-driven multiferroic states.

cond-mat.mtrl-sci↗