arXiv subjects

V. F. Mitrović

Publications and source records attributed to V. F. Mitrović.

At least 19 recordsLinked to original sources

arXiv2026

Dynamic Simulations of Strongly Coupled Spin Ensembles for Inferring Nature of Electronic Correlations from Nuclear Magnetic Resonance

We develop an efficient package for the simulation of nuclear magnetic resonance spin echo experiments to study the effects of strong electronic spin correlations on the dynamics of the nuclear spin ensemble. A mean-field model is used to study correlated electronic phases through their hyperfine interaction with nuclear spins. We explore the dynamics of the interacting nuclear ensemble and discuss the key behaviors of the system. In particular, we classify the types of temporal asymmetry that the interaction induces in the system as well as a pulse-dependent shift in the spectral domain. Using these results, we discuss how careful measurement of the pulse-dependent shift can be used to extract information about the anisotropy of the electronic interaction and how these results represent a novel tool for the examination of exotic NMR signatures in strongly correlated materials. Finally, we review specific aspects of the simulation package developed for our exploration and give explicit examples where package can be used to infer range and anisotropy of electronic correlations. In particular, we discuss its structure, accuracy, and the technical merits of the various approximations used to model the nuclear spin ensemble.

cond-mat.str-el↗

arXiv2023

Machine learning assisted determination of electronic correlations from magnetic resonance

In the presence of strong electronic spin correlations, the hyperfine interaction imparts long-range coupling between nuclear spins. Efficient protocols for the extraction of such complex information about electron correlations via magnetic response are not well known. Here, we study how machine learning can extract material parameters and help interpret magnetic response experiments. A low-dimensional representation that classifies the total interaction strength is discovered by unsupervised learning. Supervised learning generates models that predict the spatial extent of electronic correlations and the total interaction strength. Our work demonstrates the utility of artificial intelligence in the development of new probes of quantum systems, with applications to experimental studies of strongly correlated materials.

cond-mat.dis-nn↗

arXiv2023

Multi-modal spectroscopy of order parameter distributions

We present a multi-modal spectroscopic paradigm that enables independent measurement of charge and spin degrees of freedom (DOF) in strongly correlated materials. This spin-based technique probes symmetry-specific Hamiltonian parameters by analyzing how the time delay between applied pulses ($τ$) affects the response. We demonstrate ways in which charge DOF that couple through the quadrupolar interaction (inversion symmetric) can be independently measured even in the presence of large magnetic noise (inversion asymmetric). The method quantifies both the strength of the interactions and its distribution (noise). We provide protocols to directly and independently measure the distribution of interaction strengths, even when the average value of the interaction is zero. By independently measuring distributions of different forms of disorder, this methodology can elucidate which microscopic symmetry drives a phase transition. We discuss potential applications to study complex phase transitions in strongly interacting quantum materials.

cond-mat.mes-hall↗

arXiv2023

Thermal interferometry of anyons

Anyonic interferometry probes the braiding phases of excitations in topologically ordered matter. This technique is well established for charged quasiparticles in the fractional quantum Hall effect. We propose to extend it to neutral anyons, such as Ising anyons in Kitaev magnets and quasiparticles in other neutral spin liquids. We find that the thermal current through an interferometer is sensitive to the statistics of tunneling quasiparticles. We present a systematic investigation of signatures of various Abelian and non-Abelian topological orders in Fabry-Pérot and Mach-Zehnder interferometers. The heat current through a Fabry-Pérot device is different for different topological orders and depends on the topological charge inside the interferometer. A Mach-Zehnder device shows interference in topologically trivial systems only. For a non-trivial statistics, the heat current reduces to the sum of the contributions from two constrictions in the interferometer. Furthermore, we identify another probe of topological order that involves the scaling of the thermal current through a single tunneling contact at low temperatures. The current shows a universal temperature dependence, sensitive to the topological order in the system.

cond-mat.mes-hall↗

arXiv2022

Effects of charge doping on Mott insulator with strong spin-orbit coupling, Ba$_2$NaOsO$_6$

The effects of doping on the electronic evolution of the Mott insulating state have been extensively studied in efforts to understand mechanisms of emergent quantum phases of materials. The study of these effects becomes ever more intriguing in the presence of entanglement between spin and orbital degrees of freedom. Here, we present a comprehensive investigation of charge doping in the double perovskite Ba$_2$NaOsO$_6$, a a complex Mott insulator where such entanglement plays an important role. We establish that the insulating magnetic ground state evolves from canted antiferromagnet (cAF)to Néel order for dopant levels exceeding ~ 10 %. Furthermore, we determine that a broken local point symmetry (BLPS) phase, precursor to the magnetically ordered state, occupies an extended portion of the (H-T) phase diagram with increased doping. This finding reveals that the breaking of the local cubic symmetry is driven by a multipolar order, most-likely of the antiferro-quadrupolar type.

cond-mat.str-el↗

arXiv2021

Signatures of electronic correlations and spin-susceptibility anisotropy in nuclear magnetic resonance

We present a methodology for probing the details of electronic susceptibility through minimally-invasive nuclear magnetic resonance techniques. Specifically, we classify electron-mediated long-range interactions in an ensemble of nuclear spins by revealing their effect on simple spin echo experiments. We find that pulse strength and applied field orientation dependence of these spin echo measurements resolves the spatial extent and anisotropy of electronic spin susceptibility. This work provides an alternate explanation to NMR results in superconducting and magnetically-ordered systems. The methodology has direct applications for sensing and characterizing emergent electronic phases.

cond-mat.str-el↗

arXiv2021

Thermal interferometry of anyons in spin liquids

Aharonov-Bohm interferometry is the most direct probe of anyonic statistics in the quantum Hall effect. The technique involves oscillations of the electric current as a function of the magnetic field and is not applicable to Kitaev spin liquids and other systems without charged quasiparticles. Here, we establish a novel protocol, involving heat transport, for revealing fractional statistics even in the absence of charged excitations, as is the case in quantum spin liquids. Specifically, we demonstrate that heat transport in Kitaev spin liquids through two distinct interferometer geometries, Fabry-Perot and Mach-Zehnder, exhibits drastically different behaviors. Therefore, we propose the use of heat transport interferometry as a probe of anyonic statistics in charge insulators.

cond-mat.mes-hall↗

arXiv2021

Resistively detected NMR as a probe of the topological nature of conducting edge/surface states

Electron spins in edge or surface modes of topological insulators (TIs) with strong spin-orbit coupling cannot be directly manipulated with microwaves due to the locking of electron spin to its momentum. We show by contrast that a resistively detected nuclear magnetic resonance (RDNMR) based technique can be used to probe the helical nature of surface conducting states. In such experiments, one applies a radio frequency (RF) field to reorient nuclear spins that then couple to electronic spins by the hyperfine interaction. The spin of the boundary electrons can thereby be modulated, resulting in changes in conductance at nuclear resonance frequencies. Here, we demonstrate that the conductivity is sensitive to the direction of the applied magnetic field with respect to the helicity of the electrons. This dependence of the RDNMR signal on angle probes the nature of the conductive edge or surface states. In the case of 3D TI in the quantum Hall regime, we establish that the dominant mechanism responsible for the conductance change in a RDNMR experiment is based on the Overhauser field effect. Our findings indicate that the same physics underlying the use of RDNMR to probe TI states also enables us to use RF control of nuclear spins to coherently manipulate topologically protected states which could be useful for a new generation of devices.

cond-mat.mes-hall↗

arXiv2019

Evidence for orbital ordering in Ba$_2$NaOsO$_6$, a Mott insulator with strong spin orbit coupling, from First Principles

We present first principles calculations of the magnetic and orbital properties of Ba$_2$NaOsO$_6$ (BNOO), a 5$d^1$ Mott insulator with strong spin orbit coupling (SOC) in its low temperature emergent quantum phases. Our computational method takes into direct consideration recent NMR results that established that BNOO develops a local octahedral distortion preceding the formation of long range magnetic order. We found that the two-sublattice canted ferromagnetic ground state identified in Lu \etal, Nature Comm. {\bf 8}, 14407 (2017) is accompanied by a two-sublattice staggered orbital ordering pattern in which the $t_{2g}$ orbitals are selectively occupied as a result of strong spin orbit coupling. The staggered orbital order found here using first principles calculations asserts the previous proposal of Chen \etal, Phys. Rev. B {\bf 82}, 174440 (2010) and Lu \etal, Nature Comm. {\bf 8}, 14407 (2017), that two-sublattice magnetic structure is the very manifestation of staggered quadrupolar order. Therefore, our results affirm the essential role of multipolar spin interactions in the microscopic description of magnetism in systems with locally entangled spin and orbital degrees of freedom.

cond-mat.str-el↗

arXiv2017

Application of Surface Coil for Nuclear Magnetic Resonance Studies of Semi-conducting Thin Films

We conduct a comprehensive set of tests of performance of surface coils used for nuclear magnetic resonance (NMR) study of quasi 2-dimensional samples. We report ${^{115} \rm{In}}$ and ${^{31} \rm{P}}$ NMR measurements on InP, semi-conducting thin substrate samples. Surface coils of both zig-zag meander-line and concentric spiral geometries were used. We compare reception sensitivity and signal-to-noise ratio (SNR) of NMR signal obtained by using surface-type coils to that obtained by standard solenoid-type coils. As expected, we find that surface-type coils provide better sensitivity for NMR study of thin films samples. Moreover, we compare the reception sensitivity of different types of the surface coils. We identify the optimal geometry of the surface coils for a given application and/or direction of the applied magnetic field.

physics.ins-det↗

arXiv2017

Phase Diagram of Ba$_{2}$NaOsO$_{6}$, a Mott insulator with strong spin orbit interactions

We report $^{23}$Na nuclear magnetic resonance (NMR) measurements of the Mott insulator with strong spin-orbit interaction Ba$_{2}$NaOsO$_{6}$ as a function of temperature in different magnetic fields ranging from 7 T to 29 T. The measurements, intended to concurrently probe spin and orbital/lattice degrees of freedom, are an extension of our work at lower fields reported in Nat. Commun., v 8, 14407 (2017). We have identified clear quantitative NMR signatures that display the appearance of a canted ferromagnetic phase, which is preceded by local point symmetry breaking. We have compiled the field temperature phase diagram extending up to 29 T. We find that the broken local point symmetry phase extends over a wider temperature range as magnetic field increases.

cond-mat.str-el↗

arXiv2017

Nature of Lattice Distortions in Cubic Double-Perovskite Ba$_2$NaOsO$_6$

We present detailed calculations of the electric field gradient (EFG) using a point charge approximation in Ba$_2$NaOsO$_6$, a Mott insulator with strong spin-orbit interaction. Recent $^{23}$Na nuclear magnetic resonance (NMR) measurements found that the onset of local point symmetry breaking, likely caused by the formation of quadrupolar order, precedes the formation of long range magnetic order in this compound. An extension of the static $^{23}$Na NMR measurements as a function of the orientation of a 15 T applied magnetic field at 8 K in the magnetically ordered phase is reported. Broken local cubic symmetry induces a non-spherical electronic charge distribution around the Na site and thus finite EFG, affecting the NMR spectral shape. We combine the spectral analysis as a function of the orientation of the magnetic field with calculations of the EFG to determine the exact microscopic nature of the lattice distortions present in low temperature phases of this material. We establish that orthorhombic distortions, constrained along the cubic axes of the perovskite reference unit cell, of oxygen octahedra surrounding Na nuclei are present in the magnetic phase. Other common types of distortions often observed in oxide structures are considered as well.

cond-mat.str-el↗

arXiv2017

Novel Magnetism and Local Symmetry Breaking in a Mott Insulator with Strong Spin Orbit Interactions

Study of the combined effects of strong electronic correlations with spin-orbit coupling (SOC) represents a central issue in quantum materials research. Predicting emergent properties represents a huge theoretical problem since the presence of SOC implies that the spin is not a good quantum number. Existing theories propose the emergence of a multitude of exotic quantum phases, distinguishable by either local point symmetry breaking or local spin expectation values, even in materials with simple cubic crystal structure such as Ba$_2$NaOsO$_6$. Experimental tests of such theories by local probes are highly sought for. Here, we report on local measurements designed to concurrently probe spin and orbital/lattice degrees of freedom of Ba$_2$NaOsO$_6$. We find that a novel canted ferromagnetic phase which is preceded by local point symmetry breaking is stabilized at low temperatures, as predicted by quantum theories involving multipolar spin interactions.

cond-mat.str-el↗

arXiv2014

Evidence of Andreev bound states as a hallmark of the FFLO phase in $κ$-(BEDT-TTF)$_2$Cu(NCS)$_2$

Superconductivity is a quantum phenomena arising, in its simplest form, from pairing of fermions with opposite spin into a state with zero net momentum. Whether superconductivity can occur in fermionic systems with unequal number of two species distinguished by spin, atomic hyperfine states, flavor, presents an important open question in condensed matter, cold atoms, and quantum chromodynamics, physics. In the former case the imbalance between spin-up and spin-down electrons forming the Cooper pairs is indyced by the magnetic field. Nearly fifty years ago Fulde, Ferrell, Larkin and Ovchinnikov (FFLO) proposed that such imbalanced system can lead to exotic superconductivity in which pairs acquire finite momentum. The finite pair momentum leads to spatially inhomogeneous state consisting of of a periodic alternation of "normal" and "superconducting" regions. Here, we report nuclear magnetic resonance (NMR) measurements providing microscopic evidence for the existence of this new superconducting state through the observation of spin-polarized quasiparticles forming so-called Andreev bound states.

cond-mat.supr-con↗

arXiv2012

Nature of the low energy excitations in the short range ordered region of Cs$_2$CuCl$_4$ as revealed by $^{133}$Cs NMR

We report nuclear magnetic resonance measurements of the spin-1/2 anisotropic triangular lattice antiferromagnet Cs$_2$CuCl$_4$ as a function of temperature and applied magnetic field. The observed temperature and magnetic field dependence of the NMR relaxation rate suggests that low energy excitations in the short-range ordered region stabilized over a wide range of intermediate fields and temperatures of the phase diagram are gapless or nearly gapless fermionic excitations. An upper bound on the size of the gap of 0.037 meV $\approx J/10$ is established. The magnetization and NMR relaxation rate can be qualitatively described either by a quasi-1D picture of weakly coupled chains, or by mean-field theories of specific 2D spin liquids; however, quantitative differences exist between data and theory in both cases. This comparison indicates that 2D interactions are quantitatively important in describing the low-energy physics.

cond-mat.str-el↗

arXiv2009

Field Evolution of Coexisting Superconducting and Magnetic Orders in CeCoIn$_5$

We present nuclear magnetic resonance (NMR) measurements on the three distinct In sites of CeCoIn$_5$ with magnetic field applied in the [100] direction. We identify the microscopic nature of the long range magnetic order (LRO) stabilized at low temperatures in fields above 10.2 T while still in the superconducting (SC) state. We infer that the ordered moment is oriented along the $\hat c$-axis and map its field evolution. The study of the field dependence of the NMR shift for the different In sites indicates that the LRO likely coexists with a modulated SC phase, possibly that predicted by Fulde, Ferrell, Larkin, and Ovchinnikov. Furthermore, we discern a field region dominated by strong spin fluctuations where static LRO is absent and propose a revised phase diagram.

cond-mat.str-el↗

arXiv2008

Comment on ``Texture in the Superconducting Order Parameter of CeCoIn$_5$ Revealed by Nuclear Magnetic Resonance''

The study of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state has been of considerable recent interest. Below the temperature $T^*$ which is believed to be the transition temperature ($T$) to the FFLO phase in CeCoIn$_5$, K. Kakuyanagi et al. (Phys. Rev. Lett. 94, 047602 (2005)) reported a composite NMR spectrum with a tiny component observed at frequencies corresponding to the normal state signal. The results were interpreted as evidence for the emergence of an FFLO state. This result is inconsistent with two other NMR studies of V. F. Mitrovi{ć} et al. (Phys. Rev. Lett. 97, 117002 (2006)) and B.-L. Young et al. (Phys. Rev. Lett. 98, 036402 (2007)). In this comment we show that the findings of K. Kakuyanagi et al. do not reflect the true nature of the FFLO state but result from excess RF excitation power used in that experiment.

cond-mat.str-el↗

arXiv2008

Field Dependence of the Ground State in the Exotic Superconductor CeCoIn$_5$: a Nuclear Magnetic Resonance Investigation

We report $^{115}$In nuclear magnetic resonance (NMR) measurements in CeCoIn$_5$ at low temperature ($T \approx 70$ mK) as a function of magnetic field ($H_0$) from 2 T to 13.5 T applied perpendicular to the $\hat c$-axis. NMR line shift reveals that below 10 T the spin susceptibility increases as $\sqrt{H_0}$. We associate this with an increase of the density of states due to the Zeeman and Doppler-shifted quasiparticles extended outside the vortex cores in a d-wave superconductor. Above 10 T a new superconducting state is stabilized, possibly the modulated phase predicted by Fulde, Ferrell, Larkin and Ovchinnikov (FFLO). This phase is clearly identified by a strong and linear increase of the NMR shift with the field, before a jump at the first order transition to the normal state.

cond-mat.str-el↗