arXiv subjects

Christopher Sims

Publications and source records attributed to Christopher Sims.

At least 19 recordsLinked to original sources

arXiv2023

Formation of Tesseract Time Crystals on a Quantum Computer

The engineering of new states of matter through Floquet driving has revolutionized the field of condensed matter physics. This technique enables the creation of hybrid topological states and ordered phases that are absent in normal systems. Crystalline structures, exemplifying spatially ordered systems under periodic driving, have been extensively studied. However, the recent focus has shifted towards discrete time crystals (DTCs), periodically driven quantum many-body systems that break time translation symmetry under specific conditions. In this paper, we explore the theoretical predictions, experimental realizations, and emerging possibilities of utilizing DTCs on quantum computers. Additionally, the formation of time varying tesseracts using discrete time crystals is presented, allowing for the investigation of time translational symmetry in higher-dimensional lattice systems.

cond-mat.str-el↗

arXiv2023

Variational Quantum PageRank

The PageRank algorithm is used to rank web pages by their importance. Since its development, the PageRank algorithm is a critical and fundamental part of search engines today. PageRank is a graph-based algorithm that ranks pages based on how many other pages link to them. This work develops a variational quantum version of the PageRank algorithm and compares the performance of the two algorithms. It is found that quantum PageRank performs better at ranking websites than the normal PageRank algorithm

quant-ph↗

arXiv2023

Analogous Black Holes in Type-III Dirac Semimetal Ni$_3$In$_2$X$_2$ (X = S, Se)

Black holes are objects that have a large mass and curve space time, characterized by their event horizon and singularity. Recently, an interesting concept of analogous black holes has emerged in the field of condensed matter physics. In this work, the possibility of realizing analogous black holes in topological material is Ni$_3$In$_2$X$_2$ (X = S, Se) discussed. This work shows that the type-III Dirac cones of the material can lead to the emergence of an event horizon and the formation of a black hole-like region near the Dirac point. In addition, possible experimental signatures of such a system are discussed and the potential implications of an analogous black hole for the study of black hole physics in condensed matter systems.

cond-mat.mtrl-sci↗

arXiv2023

Simulation of Higher Dimensional Discrete Time Crystals on a Quantum Computer

The study of topologically ordered states have given rise to a growing interest in symmetry protected states in quantum matter. Recently, this theory has been extended to quantum many body systems which demonstrate ordered states at low temperature. An example of this is the discrete time crystal (DTC) which has been demonstrated in a real quantum computer and in driven systems. These states are periodic in time and are protected to disorder to a certain extent. In general, DTC can be classified into two phases, the stable many body localization (MBL) state, and the disordered thermal state. This work demonstrates by generalizing DTC to 2 dimensions, there is an decrease in thermal noise and an increase in the operating range of the MBL range in the presence of disorder.

cond-mat.mes-hall↗

arXiv2023

The Fractional Orbital Chern Hall Effect

The fractional quantum hall effect (FQHE) is a milestone of modern day physics, its disovery paved the way for the study of fractional charges which do not obey abelian physics. However, all FQHE require an external magnetic field in order for there to be fractionally charged electrons. This work shows a theoretical study of strongly interaction electrons in the Kagome lattice with magnetism. Under optimal conditions, a band gap opens on the surface of the material which hosts fractional Fermions. These fractional Fermions form composite quasi-electrons without the need for external magnetic field. These states are predicted to host the FQHE without the need for an external magnetic field.

cond-mat.mes-hall↗

arXiv2022

Observation of anisotropic Dirac cones in the topological material Ti2Te2P

Anisotropic bulk Dirac (or Weyl) cones in three dimensional systems have recently gained intense research interest as they are examples of materials with tilted Dirac (or Weyl) cones indicatig the violation of Lorentz invariance. In contrast, the studies on anisotropic surface Dirac cones in topological materials which contribute to anisotropic carrier mobility have been limited. By employing angle-resolved photoemission spectroscopy and first-principles calculations, we reveal the anisotropic surface Dirac dispersion in a tetradymite material Ti2Te2P on the (001) plane of the Brillioun zone. We observe the quasi-elliptical Fermi pockets at the M -point of the Brillouin zone forming the anisotropic surface Dirac cones. Our calculations of the Z2 indices confirm that the system is topologically non-trivial with multiple topological phases in the same material. In addition, the observed nodal-line like feature formed by bulk bands makes this system topologically rich.

cond-mat.mes-hall↗

arXiv2022

Highly Accurate FMRI ADHD Classification using time distributed multi modal 3D CNNs

This work proposes an algorithm for fMRI data analysis for the classification of ADHD disorders. There have been several breakthroughs in the analysis of fMRI via 3D convolutional neural networks (CNNs). With these new techniques it is possible to preserve the 3D spatial data of fMRI data. Additionally there have been recent advances in the use of 3D generative adversarial neural networks (GANs) for the generation of normal MRI data. This work utilizes multi modal 3D CNNs with data augmentation from 3D GAN for ADHD prediction from fMRI. By leveraging a 3D-GAN it would be possible to use deepfake data to enhance the accuracy of 3D CNN classification of brain disorders. A comparison will be made between a time distributed single modal 3D CNN model for classification and the modified multi modal model with MRI data as well.

cs.LG↗

arXiv2022

Existence of Chern Gaps in Kagome Magnets RMn$_6$Ge$_6$ (R = Nd, Sm, Tb, Dy, Ho, Er, Yb, Lu)

Kagome Chern Magnets are lattices which host a Chern state when they are non-magnetic and a Chern Gap when they become magnetic. These Chern gaps can host fractional Chern Fermions. There has been extensive research in the RMn$_6$Sn$_6$ system which hosts a small Chern gap with many trivial bands surrounding them. RMn$_6$Ge$_6$ is studied theoretically in order to find a more insulating Kagome magnetic with fewer bands near the Chern gap.

cond-mat.str-el↗

arXiv2022

Edge Detection and Image Filter algorithms for Spectroscopic Analysis with Deep Learning Applications

Edge detection and image filters are commonly used in computer vision. However, they have never been applied to the data analysis of angle-resolved photoemission spectroscopy (ARPES) data before in a systematic fashion. In this paper we will use the Sobel, Laplacian of a gaussian (LoG), Canny, Prewitt, Roberts, and fuzzy logic methods for edge detection in the ARPES results of HfP2, ZrSiS, and Hf2Te2P2. We find that the Canny filter is the best method for edge detection of noisy data that is typical of ARPES measurements, while the other edge detection techniques are not able to correctly detect ARPES bands.

cond-mat.mtrl-sci↗

arXiv2022

SpectroLab: An Open Source Matlab Based Toolbox for High Throughput Spectroscopy Analysis

We present an open source software package SpectroLab a Matlab-based tool developed in 2018 for the analysis of spectroscopic data. In this package, there are tools for derivative analysis, stacked energy contours, stacked plots for theory, 3D volumetric plots, core level analysis, and derivative analysis. The package can currently be used for angle-resolved photoemission spectroscopy (ARPES) data, with the ability to also be used for other spectroscopic data in the future. We apply this program to the HfP2, ZrSiS, and Hf2Te2P systems to demonstrate its robustness.

cond-mat.mtrl-sci↗

arXiv2021

Anisotropically large anomalous and topological Hall effect in a kagome magnet

Recently, kagome materials have become an engrossing platform to study the interplay among symmetry, magnetism, topology, and electron correlation. The latest works on RMn6Sn6 (R = rare earth metal) compounds have illustrated that this family could be intriguing to investigate various physical phenomena due to large spin-orbit coupling and strong magnetic ordering. However, combined transport and spectroscopic studies in RMn6Sn6 materials are still limited. Here, we report magnetic, magneto-transport, and angle-resolved photoemission spectroscopy measurements of a kagome magnet ErMn6Sn6 that undergoes antiferromagnetic (TN = 345 K) to ferrimagnetic (TC = 68 K) phase transitions in the presence of field. We observe large anomalous and topological Hall effects serving as transport signatures of the nontrivial Berry curvature. The isothermal magnetization exhibits strong anisotropic nature and the topological Hall effect of the compound depends on the critical field of metamagnetic transition. Our spectroscopic results complemented by theoretical calculations show the multi-orbital kagome fermiology. This work provides new insight into the tunability and interplay of topology and magnetism in a kagome magnet.

cond-mat.mes-hall↗

arXiv2021

Evolution of the Chern Gap in Chern Magnet HoMn$_6$Sn$_{6-x}$Ge$_x$

The Chern gap is a unique topological feature that can host non-abelian particles. The Kagome lattice forms a chern insulator with no gap. Upon the inclusion of magnetism the Kagome system hosts a Chern gap at the K points in the lattice. In this work, the effect of Ge doping on HoMn$_6$Sn$_{6}$ is investigated. It is seen that with increased doping, a multi-stack Chern gap in formed in HoMn$_6$Sn$_{6-x}$Ge$_x$. In addition, the Chern gaps are much more pronounced and larger in energy in HoMn$_6$Ge$_{6}$ then HoMn$_6$Sn$_{6}$.

cond-mat.str-el↗

arXiv2020

Observation of gapped state in rare-earth monopnictide HoSb

The rare-earth monopnictide family is attracting an intense current interest driven by its unusual extreme magnetoresistance (XMR) property and the potential presence of topologically non-trivial surface states. The experimental observation of non-trivial surface states in this family of materials are not ubiquitous. Here, using high-resolution angle-resolved photoemission spectroscopy (ARPES), magnetotransport, and parallel first-principles modeling, we examine the nature of electronic states in HoSb. Although we find the presence of bulk band gaps at the G and X-symmetry points of the Brillouin zone (BZ), we do not find these gaps to exhibit band inversion so that HoSb does not host a Dirac semimetal state. Our magnetotransport measurements indicate that HoSb can be characterized as a correlated nearly-complete electron-hole-compensated semimetal. Our analysis reveals that the nearly perfect electron-hole compensation could drive the appearance of non-saturating XMR effect in HoSb.

cond-mat.mes-hall↗

arXiv2020

Topologically Protected Wormholes in Type-III Weyl Semimetal Co$_3$In$_2$X$_2$ (X = S, Se)

The observation of wormholes has proven to be difficult in the field of astrophysics. However, with the discovery of novel topological quantum materials it is possible to observe astrophysical and particle physics effects in condensed matter physics. It is proposed in this work that wormholes can exist in a type-III Weyl phase. In addition, these wormholes are topologically protected, making them feasible to create and measure in condensed matter systems. Finally, Co$_3$In$_2$X$_2$ (X = S, Se) are identified as ideal type-III Weyl semimetals and experiments are put forward to confirm the existence of a type-III Weyl phase.

cond-mat.str-el↗

arXiv2020

Effect of dilute magnetism in a topological insulator

Three-dimensional topological insulators (TIs) have emerged as a unique state of quantum matter and generated enormous interests in condensed matter physics. The surfaces of a three dimensional (3D) TI are composed of a massless Dirac cone, which is characterized by the Z2 topological invariant. Introduction of magnetism on the surface of TI is essential to realize the quantum anomalous Hall effect (QAHE) and other novel magneto-electric phenomena. Here, by using a combination of first principles calculations, magneto-transport, angle-resolved photoemission spectroscopy (ARPES), and time resolved ARPES (tr-ARPES), we study the electronic properties of Gadolinium (Gd) doped Sb2Te3. Our study shows that Gd doped Sb2Te3 is a spin-orbit-induced bulk band-gap material, whose surface is characterized by a single topological surface state. We further demonstrate that introducing diluted 4f-electron magnetism into the Sb2Te3 topological insulator system by the Gd doping creates surface magnetism in this system. Our results provide a new platform to investigate the interaction between dilute magnetism and topology in doped topological materials.

cond-mat.mes-hall↗

arXiv2020

CIF2WAN: A Tool to Generate Input Files for Electronic Structure Calculations with Wannier90

The generation of input files for density functional theory (DFT) programs must often be manually done by researchers. If one wishes to produce a maximally localized wannier functions (MLWFs) the calculation consists of several separate files that must be formatted correctly in order for the program to work properly. Many of the inputs are repeated throughout the files and can be easily automated. In this work, a program is presented to generate all of the input files needed to produce wannier functions with Wannier90 starting from open source DFT programs such as Quantum Espresso, Abinit, and Siesta. In addition, the input files for WannierTools are also included for those that wish to produce surface green's functions for the generation of surface state bands. The program presented allows for users new to DFT to use the programs with minimal understanding of parameters needed to produce good results, in addition, this program allows for researchers who are advanced DFT users to utilize this program for high throughput wannier calculations.

physics.comp-ph↗

arXiv2019

Observation of multiple Dirac states in a magnetic topological material EuMg2Bi2

Initiated by the discovery of topological insulators, topologically non-trivial materials, more specifically topological semimetals and metals have emerged as new frontiers in the field of quantum materials. In this work, we perform a systematic measurement of EuMg2Bi2, a compound with antiferromagnetic transition temperature at 6.7 K, observed via electrical resistivity, magnetization and specific heat capacity measurements. By utilizing angle-resolved photoemission spectroscopy in concurrence with first-principles calculations, we observe Dirac cones at the corner and the zone center of the Brillouin zone. From our experimental data, multiple Dirac states at G and K points are observed, where the Dirac nodes are located at different energy positions from the Fermi level. Our experimental investigations of detailed electronic structure as well as transport measurements of EuMg2Bi2 suggest that it could potentially provide a platform to study the interplay between topology and magnetism.

cond-mat.mes-hall↗

arXiv2019

Observation of topological surface state in a superconducting material

The discovery of topological insulator phase has ignited massive research interests in novel quantum materials. Topological insulators with superconductivity further invigorate the importance of materials providing the platform to study the interplay between these two unique states. However, the candidates of such materials are rare. Here, we report a systematic angle-resolved photoemission spectroscopy (ARPES) study of a superconducting material CaBi2 [Tc = 2 K], corroborated by the first principles calculations. Our study reveals the presence of Dirac cones with a topological protection in this system. Systematic topological analysis based on symmetry indicator shows the presence of weak topological indices in this material. Furthermore, our transport measurements show the presence of large magnetoresistance in this compound. Our results indicate that CaBi2 could potentially provide a material platform to study the interplay between superconductivity and topology.

cond-mat.mes-hall↗