Showing papers on "Elementary particle published in 2018"
TL;DR: In this article, an improved experimental limit on the electric dipole moment of the electron was obtained by measuring the electron spin precession in a superposition of quantum states of electrons subjected to a huge intramolecular electric field.
Abstract: The standard model of particle physics accurately describes all particle physics measurements made so far in the laboratory. However, it is unable to answer many questions that arise from cosmological observations, such as the nature of dark matter and why matter dominates over antimatter throughout the Universe. Theories that contain particles and interactions beyond the standard model, such as models that incorporate supersymmetry, may explain these phenomena. Such particles appear in the vacuum and interact with common particles to modify their properties. For example, the existence of very massive particles whose interactions violate time-reversal symmetry, which could explain the cosmological matter–antimatter asymmetry, can give rise to an electric dipole moment along the spin axis of the electron. No electric dipole moments of fundamental particles have been observed. However, dipole moments only slightly smaller than the current experimental bounds have been predicted to arise from particles more massive than any known to exist. Here we present an improved experimental limit on the electric dipole moment of the electron, obtained by measuring the electron spin precession in a superposition of quantum states of electrons subjected to a huge intramolecular electric field. The sensitivity of our measurement is more than one order of magnitude better than any previous measurement. This result implies that a broad class of conjectured particles, if they exist and time-reversal symmetry is maximally violated, have masses that greatly exceed what can be measured directly at the Large Hadron Collider.
691 citations
TL;DR: Gigorov et al. as discussed by the authors advocate for the construction of a new detector element at the LHCb experiment, designed to search for displaced decays of beyond Standard Model long-lived particles.
Abstract: Author(s): Gligorov, VV; Knapen, S; Papucci, M; Robinson, DJ | Abstract: We advocate for the construction of a new detector element at the LHCb experiment, designed to search for displaced decays of beyond Standard Model long-lived particles, taking advantage of a large shielded space in the LHCb cavern that is expected to soon become available. We discuss the general features and putative capabilities of such an experiment, as well as its various advantages and complementarities with respect to the existing LHC experiments and proposals such as SHiP and MATHUSLA. For two well-motivated beyond Standard Model benchmark scenarios - Higgs decay to dark photons and B meson decays via a Higgs mixing portal - the reach either complements or exceeds that predicted for other LHC experiments.
293 citations
TL;DR: In this article, a measurement of the H→ττ signal strength is performed using events recorded in proton-proton collisions by the CMS experiment at the LHC in 2016 at a center-of-mass energy of 13TeV.
250 citations
TL;DR: This work opens up a new area of research on the fundamental gravitational properties of protons, neutrons and nuclei, which can provide access to their physical radii, the internal shear forces acting on the quarks and their pressure distributions.
Abstract: The proton, one of the components of atomic nuclei, is composed of fundamental particles called quarks and gluons. Gluons are the carriers of the force that binds quarks together, and free quarks are never found in isolation—that is, they are confined within the composite particles in which they reside. The origin of quark confinement is one of the most important questions in modern particle and nuclear physics because confinement is at the core of what makes the proton a stable particle and thus provides stability to the Universe. The internal quark structure of the proton is revealed by deeply virtual Compton scattering1,2, a process in which electrons are scattered off quarks inside the protons, which subsequently emit high-energy photons, which are detected in coincidence with the scattered electrons and recoil protons. Here we report a measurement of the pressure distribution experienced by the quarks in the proton. We find a strong repulsive pressure near the centre of the proton (up to 0.6 femtometres) and a binding pressure at greater distances. The average peak pressure near the centre is about 1035 pascals, which exceeds the pressure estimated for the most densely packed known objects in the Universe, neutron stars3. This work opens up a new area of research on the fundamental gravitational properties of protons, neutrons and nuclei, which can provide access to their physical radii, the internal shear forces acting on the quarks and their pressure distributions. Measurements of the quark pressure distribution in the proton reveal a strong repulsive pressure near the proton’s centre (stronger than the pressure in neutron stars) and a binding pressure at greater distances.
224 citations
TL;DR: The first observation of electroweak production of same-sign W boson pairs in proton-proton collisions was reported in this article, where the data sample corresponds to an integrated luminosity of 359 fb^(−1) collected at a center-of-mass energy of 13 TeV with the CMS detector at the LHC Events are selected by requiring exactly two leptons (electrons or muons) of the same charge, moderate missing transverse momentum, and two jets with a large rapidity separation and a large dijet mass.
Abstract: The first observation of electroweak production of same-sign W boson pairs in proton-proton collisions is reported The data sample corresponds to an integrated luminosity of 359 fb^(−1) collected at a center-of-mass energy of 13 TeV with the CMS detector at the LHC Events are selected by requiring exactly two leptons (electrons or muons) of the same charge, moderate missing transverse momentum, and two jets with a large rapidity separation and a large dijet mass The observed significance of the signal is 55 standard deviations, where a significance of 57 standard deviations is expected based on the standard model The ratio of measured event yields to that expected from the standard model at leading order is 090 ± 022 A cross section measurement in a fiducial region is reported Bounds are given on the structure of quartic vector boson interactions in the framework of dimension-8 effective field theory operators and on the production of doubly charged Higgs bosons
151 citations
TL;DR: A method to probe new long- and intermediate-range interactions using precision atomic isotope shift spectroscopy and a formalism to interpret linear King plots as bounds on new physics with minimal theory inputs are explored.
Abstract: We explore a method to probe new long- and intermediate-range interactions using precision atomic isotope shift spectroscopy. We develop a formalism to interpret linear King plots as bounds on new physics with minimal theory inputs. We focus only on bounding the new physics contributions that can be calculated independently of the standard model nuclear effects. We apply our method to existing Ca^{+} data and project its sensitivity to conjectured new bosons with spin-independent couplings to the electron and the neutron using narrow transitions in other atoms and ions, specifically, Sr and Yb. Future measurements are expected to improve the relative precision by 5 orders of magnitude, and they can potentially lead to an unprecedented sensitivity for bosons within the 0.3 to 10 MeV mass range.
138 citations
TL;DR: In this article, the authors present a number of tight and unexpected correlations between selected properties of the dark and the luminous matter, which leads to a dark particle able to interact with the Standard Model particles over cosmological times, and whether we need a paradigm shift from pure collisionless dark particles emerging from "first principles", to particles that we can discover only by looking to how they have designed the structure of the galaxies.
Abstract: The distribution of the non-luminous matter in galaxies of different luminosity and Hubble type is much more than a proof of the existence of dark particles governing the structures of the Universe. Here, we will review the complex but well-ordered scenario of the properties of the dark halos also in relation with those of the baryonic components they host. Moreover, we will present a number of tight and unexpected correlations between selected properties of the dark and the luminous matter. Such entanglement evolves across the varying properties of the luminous component and it seems to unequivocally lead to a dark particle able to interact with the Standard Model particles over cosmological times. This review will also focus on whether we need a paradigm shift, from pure collisionless dark particles emerging from "first principles", to particles that we can discover only by looking to how they have designed the structure of the galaxies. \keywords{Dark matter \and Galaxies \and Cosmology \and Elementary particles}
130 citations
TL;DR: In this article, a search for an invisibly decaying Higgs boson or dark matter candidates produced in association with a leptonically decaying Z boson in proton-proton collisions at s = 13 TeV is presented.
115 citations
TL;DR: An inclusive search for the standard model Higgs boson produced with large transverse momentum (p_{T}) and decaying to a bottom quark-antiquark pair (bb[over ¯]) is performed using a data set of pp collisions collected with the CMS experiment at the LHC.
Abstract: An inclusive search for the standard model Higgs boson (H) produced with large transverse momentum (p_T) and decaying to a bottom quark-antiquark pair (bb) is performed using a data set of pp collisions at √s = 13 TeV collected with the CMS experiment at the LHC. The data sample corresponds to an integrated luminosity of
35.9 fb^(−1). A highly Lorentz-boosted Higgs boson decaying to bb is reconstructed as a single, large radius jet, and it is identified using jet substructure and dedicated b tagging techniques. The method is validated with Z → bb decays. The Z → bb process is observed for the first time in the single-jet topology with a local significance of 5.1 standard deviations (5.8 expected). For a Higgs boson mass of 125 GeV, an excess of events above the expected background is observed (expected) with a local significance of 1.5 (0.7) standard deviations. The measured cross section times branching fraction for production via gluon fusion of H → bb with reconstructed p_T > 450 GeV and in the pseudorapidity range −2.5 < η < 2.5 is 74 ± 48 (stat)^(+17)_(−10)(syst) fb, which is consistent within uncertainties with the standard model prediction.
106 citations
TL;DR: In this paper, a simple extension of the Standard Model with flavor-dependent charge was proposed to explain some of B-meson anomalies recently reported at LHCb, and various bounds on the extended Higgs sector from Higgs and electroweak precision data were imposed.
Abstract: We consider a simple extension of the Standard Model with flavor-dependent $$U(1)'$$
, that has been proposed to explain some of B-meson anomalies recently reported at LHCb. The $$U(1)'$$
charge is chosen as a linear combination of anomaly-free $$B_3-L_3$$
and $$L_\mu -L_\tau $$
. In this model, the flavor structure in the SM is restricted due to flavor-dependent $$U(1)'$$
charges, in particular, quark mixings are induced by a small vacuum expectation value of the extra Higgs doublet. As a result, it is natural to get sizable flavor-violating Yukawa couplings of heavy Higgs bosons involving the bottom quark. In this article, we focus on the phenomenology of the Higgs sector of the model including extra Higgs doublet and singlet scalars. We impose various bounds on the extended Higgs sector from Higgs and electroweak precision data, B-meson mixings and decays as well as unitarity and stability bounds, then discuss the productions and decays of heavy Higgs bosons at the LHC.
74 citations
TL;DR: In this article, vector boson fusion was studied at high energy lepton colliders and it was shown that CLIC has the potential to test single production cross-sections of a few tens of attobarns in di-Higgs and di-boson final states.
Abstract: We study vector boson fusion production of new scalar singlets at high energy lepton colliders. We find that CLIC has the potential to test single production cross-sections of a few tens of attobarns in di-Higgs and di-boson final states. In models with a sizeable singlet-Higgs mixing, these values correspond to a precision in Higgs couplings of order 0.1% or better. We compare our sensitivities with those of the LHC and interpret our results in well-motivated models like the Twin Higgs, the NMSSM and axion-like particles. Looking forward to even higher energy machines, we show that the reach of muon colliders like LEMMA or MAP overcomes the one of future hadron machines like FCC-hh. We finally study the pair production of the new scalar singlets via an off-shell Higgs. This process does not vanish for small mixings and will constitute a crucial probe of models generating a first order electro-weak phase transition.
TL;DR: In this article, the electroweak phase transition in the alignment limit of the CP-conserving two-Higgs-doublet model (2HDM) of Type I and Type II was studied.
Abstract: We study the electroweak phase transition in the alignment limit of the CP-conserving two-Higgs-doublet model (2HDM) of Type I and Type II. The effective potential is evaluated at one-loop, where the thermal potential includes Daisy corrections and is reliably approximated by means of a sum of Bessel functions. Both 1-stage and 2-stage electroweak phase transitions are shown to be possible, depending on the pattern of the vacuum development as the Universe cools down. For the 1-stage case focused on in this paper, we analyze the properties of phase transition and discover that the field value of the electroweak symmetry breaking vacuum at the critical temperature at which the first order phase transition occurs is largely correlated with the vacuum depth of the 1-loop potential at zero temperature. We demonstrate that a strong first order electroweak phase transition (SFOEWPT) in the 2HDM is achievable and establish benchmark scenarios leading to different testable signatures at colliders. In addition, we verify that an enhanced triple Higgs coupling (including loop corrections) is a typical feature of the SFOPT driven by the additional doublet. As a result, SFOEWPT might be able to be probed at the LHC and future lepton colliders through Higgs pair production.
TL;DR: In this article, the covariant DeWitt-Brehme (DWB) equation is reduced to a covariant form of the Lorenz-Dirac (LD) equation.
Abstract: In many astrophysically relevant situations, radiation-reaction forces acting upon a charge cannot be ignored, and the question of the location and stability of circular orbits in such a regime arises. The motion of a point charge with radiation reaction in flat spacetime is described by the Lorenz–Dirac (LD) equation, while in curved spacetime it is described by the DeWitt–Brehme (DWB) equation containing the Ricci term and a tail term. We show that for the motion of elementary particles in vacuum metrics, the DWB equation can be reduced to the covariant form of the LD equation, which we use here. Generically, the LD equation is plagued by runaway solutions, so we discuss computational ways of avoiding this problem when constructing numerical solutions. We also use the first iteration of the covariant LD equation, which is the covariant Landau–Lifshitz equation, comparing the results of these two approaches and showing the smallness of the third-order Schott term in the ultrarelativistic case. We calculate the corresponding energy and angular momentum loss of a particle and study the damping of charged particle oscillations around an equilibrium radius. We find that, depending on the orientation of the Lorentz force, the oscillating charged particle either spirals down to the black hole or stabilizes the circular orbit by decaying its oscillations. The latter case leads to the interesting new result of the particle orbit shifting outwards from the black hole. We also discuss the astrophysical relevance of the presented approach and provide estimates of the main parameters of the model.
TL;DR: In this article, two inter-related mechanisms operative in the electroweak sector of the Standard Model at high energies are introduced and discussed, and the effects of Higgsplosion alter quantum corrections from very heavy states to the Higgs boson mass.
TL;DR: In this paper, a neural network was used to improve the background rejection and extract the signal of top quark production in the collision data collected by the ATLAS experiment at the LHC in 2015 and 2016.
TL;DR: In this paper, the authors studied the missing energy signature for the A → i n v i s i b l e decay that allows to probe the γ − A − mixing strength in a wide, from sub-MeV to sub-GeV, A − mass range.
TL;DR: In this article, the location and stability of circular orbits in a curved spacetime regime were investigated. And the covariant form of the DeWitt-Brehme (DWB) equation was shown to be a covariant version of the Lorenz-Dirac (LD) equation.
Abstract: In many astrophysically relevant situations radiation reaction force acting upon a charge can not be neglected and the question arises about the location and stability of circular orbits in such regime. Motion of point charge with radiation reaction in flat spacetime is described by Lorenz-Dirac (LD) equation, while in curved spacetime -- by DeWitt-Brehme (DWB) equation containing the Ricci term and the tail term. We show that for the motion of elementary particles in vacuum metrics the DWB equation can be reduced to the covariant form of the LD equation which we use here. Generically, the LD equation is plagued by runaway solutions, so we discuss computational ways to avoid this problem in constructing numerical solutions. We also use the first iteration of the covariant LD equation which is the covariant Landau-Lifshitz equation, comparing results of these two approaches and showing smallness of the third-order Schott term in the ultrarelativistic case. We calculate the corresponding energy and angular momentum loss of a particle and study the damping of charged particle oscillations around an equilibrium radius. We find that depending on the orientation of the Lorentz force, the oscillating charged particle either spirals down to the black hole, or stabilizes the circular orbit by decaying its oscillations. The later case leads to an interesting new result of shifting of the particle orbit outwards from the black hole. We also discuss the astrophysical relevance of the presented approach and provide estimations of the main parameters of the model.
TL;DR: In this article, it was shown how twisting the spectral triple of the Standard Model of elementary particles naturally yields the Krein space associated with the Lorentzian signature of spacetime.
Abstract: We show how twisting the spectral triple of the Standard Model of elementary particles naturally yields the Krein space associated with the Lorentzian signature of spacetime. We discuss the associated spectral action, both for fermions and bosons. What emerges is a tight link between twists and Wick rotation.
TL;DR: In this paper, the authors proposed a non-supersymmetric flipped non-minimal particle content model based on the minimal particle content principle, which can be constructed from the four-dimensional SO(10) models, five-dimensional orbifold SO( 10) models and local F-theory SO(12) models.
Abstract: Giving up the solutions to the fine-tuning problems, we propose the non-supersymmetric flipped $$SU(5)\times U(1)_X$$
model based on the minimal particle content principle, which can be constructed from the four-dimensional SO(10) models, five-dimensional orbifold SO(10) models, and local F-theory SO(10) models. To achieve gauge coupling unification, we introduce one pair of vector-like fermions, which form a complete $$SU(5)\times U(1)_X$$
representation. The proton lifetime is around $$5\times 10^{35}$$
years, neutrino masses and mixing can be explained via the seesaw mechanism, baryon asymmetry can be generated via leptogenesis, and the vacuum stability problem can be solved as well. In particular, we propose that inflaton and dark matter particles can be unified to a real scalar field with $$Z_2$$
symmetry, which is not an axion and does not have the non-minimal coupling to gravity. Such a kind of scenarios can be applied to the generic scalar dark matter models. Also, we find that the vector-like particle corrections to the $$B_s^0$$
masses might be about 6.6%, while their corrections to the $$K^0$$
and $$B_d^0$$
masses are negligible.
TL;DR: This essay reminisce about the forerunners of the standard model, the beginnings of the model half a century ago, and its development and confirmation from then to the present.
Abstract: The standard model is a quantum field theory that successfully accounts for the strong, weak, and electromagnetic interactions of the known elementary particles. In this essay I reminisce about the forerunners of the standard model, the beginnings of the model half a century ago, and its development and confirmation from then to the present.
TL;DR: In this paper, it was shown that in a theory where the low energy dynamics of the gravitons are governed by the Einstein-Hilbert action, any finite number of massive elementary higher spin particles with spin more than two cannot interact with gravity in a way that preserves causality.
Abstract: According to common lore, massive elementary higher spin particles lead to inconsistencies when coupled to gravity. However, this scenario was not completely ruled out by previous arguments. In this paper, we show that in a theory where the low energy dynamics of the gravitons are governed by the Einstein-Hilbert action, any finite number of massive elementary particles with spin more than two cannot interact with gravitons, even classically, in a way that preserves causality. This is achieved in flat spacetime by studying eikonal scattering of higher spin particles in more than three spacetime dimensions. Our argument is insensitive to the physics above the effective cut-off scale and closes certain loopholes in previous arguments. Furthermore, it applies to higher spin particles even if they do not contribute to tree-level graviton scattering as a consequence of being charged under a global symmetry such as $\mathbb{Z}_2$. We derive analogous bounds in anti-de Sitter spacetime from analyticity properties of correlators of the dual CFT in the Regge limit. We also argue that an infinite tower of fine-tuned higher spin particles can still be consistent with causality. However, they necessarily affect the dynamics of gravitons at an energy scale comparable to the mass of the lightest higher spin particle. Finally, we apply the bound in de Sitter to impose restrictions on the structure of three-point functions in the squeezed limit of the scalar curvature perturbation produced during inflation.
26 Oct 2018
TL;DR: In this article, a low-energy effective theory of atwo-dimensional vortex lattice in a bosonic Galilean-invariant compressiblesuperfluid was formulated using boson-vortex duality.
Abstract: Using boson-vortex duality, we formulate a low-energy effective theory of atwo-dimensional vortex lattice in a bosonic Galilean-invariant compressiblesuperfluid. The excitation spectrum contains a gapped Kohn mode and anelliptically polarized Tkachenko mode that has quadratic dispersion relation atlow momenta. External rotation breaks parity and time-reversal symmetries andgives rise to Hall responses. We extract the particle number current and stresstensor linear responses and investigate the relations between them that followfrom Galilean symmetry. We argue that elementary particles and vortices do notcouple to the spin connection which suggests that the Hall viscosity at zerofrequency and momentum vanishes in a vortex lattice.
TL;DR: The Higgs mechanism is one of the central pieces of the Standard Model of electroweak interactions and thanks to it we can generate the masses of the elementary particles as mentioned in this paper. But its fundamental origin is unknown.
Abstract: The Higgs mechanism is one of the central pieces of the Standard Model of electroweak interactions and thanks to it we can generate the masses of the elementary particles. Its fundamental origin is...
TL;DR: In this paper, the authors consider the Minimal Supersymmetric extension of the Standard Model in the regime where the supersymmetric breaking scale is extremely large and evaluate the next-to-leading order radiative corrections to the two neutral CP-even Higgs self-couplings λ H h h and λ h h h.
TL;DR: A one-dimensional generalized lattice Wilson-Dirac fermion model is proposed and it is found that the model exhibits nontrivial topological phases characterized by gapless edge modes and a finite winding number in the broad regime of the parameter space.
Abstract: The Dirac fermion is an important fundamental particle appearing in high-energy physics and topological insulator physics. In particular, a Dirac fermion in a one-dimensional lattice system exhibits the essential properties of topological physics. However, the system has not been quantum simulated in experiments yet. Herein, we propose a one-dimensional generalized lattice Wilson-Dirac fermion model and study its topological phase structure. We show the experimental setups of an atomic quantum simulator for the model, in which two parallel optical lattices with the same tilt for trapping cold fermion atoms and a laser-assisted hopping scheme are used. Interestingly, we find that the model exhibits nontrivial topological phases characterized by gapless edge modes and a finite winding number in the broad regime of the parameter space. Some of the phase diagrams closely resemble those of the Haldane model. We also discuss topological charge pumping and a lattice Gross-Neveu model in the system of generalized Wilson-Dirac fermions.
INAF1
TL;DR: In this paper, the authors derived the corresponding photon survival probability P γ → γ ALP (E 0, z ) analytically and exactly up to observed energies E 0 = 1000 TeV and redshift up to z = 2, a fact that drastically shortens the computation time in the derivation of the results presented in this paper.
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TL;DR: In this article, the authors revisited the derivation of Heisenberg's uncertainty principle and showed how the principle collapsed at the Planck scale by introducing a minor modification, which does not change the main equations in quantum mechanics; it only gives them a Planck-scale limit where uncertainty collapses.
Abstract: In this paper, we will revisit the derivation of Heisenberg’s uncertainty principle. We will see how the Heisenberg principle collapses at the Planck scale by introducing a minor modification. The beauty of our suggested modification is that it does not change the main equations in quantum mechanics; it only gives them a Planck scale limit where uncertainty collapses. We suspect that Einstein could have been right after all, when he stated, “God does not throw dice.” His now-famous saying was an expression of his skepticism towards the concept that quantum randomness could be the ruling force, even at the deepest levels of reality. Here we will explore the quantum realm with a fresh perspective, by re-deriving the Heisenberg principle in relation to the Planck scale. We will show how this idea also leads to an upper boundary on uncertainty, in addition to the lower boundary. These upper and lower boundaries are identical for the Planck mass particle; in fact, they are zero, and this highlights the truly unique nature of the Planck mass particle. Further, there may be a close connection between light and the Planck mass particle: In our model, the standard relativistic energy momentum relation also seems to apply to light, while in modern physics light generally stands outside the standard relativistic momentum energy relation. We will also suggest a new way to look at elementary particles, where mass and time are closely related, consistent with some of the recent work in experimental physics. Our model leads to a new time operator that does not appear to be in conflict with the Pauli objection. This indicates that both mass and momentum come in quanta, which are perfectly correlated to an internal Compton ‘clock’ frequency in elementary particles.
01 May 2018
TL;DR: In this article, the authors revisited the derivation of Heisenberg's uncertainty principle and showed how the principle collapsed at the Planck scale by introducing a minor modification, which does not change the main equations in quantum mechanics; it only gives them a Planck-scale limit where uncertainty collapses.
Abstract: In this paper, we will revisit the derivation of Heisenberg’s uncertainty principle. We will see how the Heisenberg principle collapses at the Planck scale by introducing a minor modification. The beauty of our suggested modification is that it does not change the main equations in quantum mechanics; it only gives them a Planck scale limit where uncertainty collapses. We suspect that Einstein could have been right after all, when he stated, “God does not throw dice.” His now-famous saying was an expression of his skepticism towards the concept that quantum randomness could be the ruling force, even at the deepest levels of reality. Here we will explore the quantum realm with a fresh perspective, by re-deriving the Heisenberg principle in relation to the Planck scale. We will show how this idea also leads to an upper boundary on uncertainty, in addition to the lower boundary. These upper and lower boundaries are identical for the Planck mass particle; in fact, they are zero, and this highlights the truly unique nature of the Planck mass particle. Further, there may be a close connection between light and the Planck mass particle: In our model, the standard relativistic energy momentum relation also seems to apply to light, while in modern physics light generally stands outside the standard relativistic momentum energy relation. We will also suggest a new way to look at elementary particles, where mass and time are closely related, consistent with some of the recent work in experimental physics. Our model leads to a new time operator that does not appear to be in conflict with the Pauli objection. This indicates that both mass and momentum come in quanta, which are perfectly correlated to an internal Compton ‘clock’ frequency in elementary particles.
TL;DR: The results of searches for new elementary particles that decay into boson pairs (dibosons) performed at the CERN Large Hadron Collider in proton-proton collision data collected by the ATLAS and CMS experiments at 7-, 8-, and 13-TeV center-of-mass energy until the year 2017 are reviewed in this paper.
23 Oct 2018
TL;DR: In this paper, the spin-momentum locking was applied to two classes of materials, oxide interfaces and Weyl semimetals, with a focus on their electrical transport properties.
Abstract: Electrons in a crystal lattice have properties that may
differ from those of a free electron in vacuum. The effective mass can be
different from the bare electron mass, and it may even vanish, so that the electron behaves in some respects as a relativistic massless
particle such as a photon. The magnetic moment of the intrinsic angular
momentum, the electron spin, may be also different from that of an elementary particle. Spin-like degrees
of freedom, referred to as "pseudospin" or "valley
isospin", can also arise in the effective low-energy description of electrons in the lattice fields.
These various degrees of freedom are of interest as ways to store and
transport information: one speaks of "spintronics" and
"valleytronics" as alternatives to "electronics".
For these purposes it is of interest to study the interplay between the
orbital motion of electrons and their spin (spin-like) degrees of freedom, the so-called "spin-orbit coupling". In some systems where this interaction is strong, it causes the electron spin
to be tied to the direction of motion.
This thesis contains results about the effects of this "spin-momentum
locking" on two classes of materials, oxide interfaces
and Weyl semimetals, with a focus on their electrical transport properties.