arXiv subjects

Thibaut Jonckheere

Publications and source records attributed to Thibaut Jonckheere.

At least 37 records · Page 2Linked to original sources

arXiv2018

Crystallization of Levitons in the fractional quantum Hall regime

Using a periodic train of Lorentzian voltage pulses, which generates soliton-like electronic excitations called Levitons, we investigate the charge density backscattered off a quantum point contact in the fractional quantum Hall regime. We find a regular pattern of peaks and valleys, reminiscent of analogous self-organization recently observed for optical solitons in non-linear environments. This crystallization phenomenon is confirmed by additional side dips in the Hong-Ou-Mandel noise, a feature that can be observed in nowadays electron quantum optics experiments.

cond-mat.mes-hall↗

arXiv2018

DC-current induced domain wall in a chiral $p$-wave superconductor

We study theoretically the impact of an applied DC-current on a mesoscopic chiral $p$-wave superconductor. Performing quasiclassical calculations on a two-dimensional system, with an external magnetic flux to generate a DC current, we show that the current can trigger a transition to a state with a domain wall between regions of different chiralities. The system shows an hysteretic behavior, as different domain wall configurations are possible for a given current. This domain wall creation mechanism can give new insights on recent experiments observing anomalous current variations in Sr${}_2$RuO${}_4$ junctions.

cond-mat.supr-con↗

arXiv2018

Probing interactions via non-equilibrium momentum distribution and noise in integer quantum Hall systems at $ν=2$

We consider the excitation of single-electron wave packets by means of a time dependent voltage applied to the ballistic edge channels of the integer quantum Hall effect at filling factor $ν=2$. Due to electron-electron interactions, fractional excitations emerge along the edge. Their detailed structure is analyzed by evaluating the nonequilibrium momentum distributions associated with the different edge channels. We provide results for a generic time-dependent drive both in the stationary regime and for intermediate times, where the overlap between fractionalized wave packets carries relevant information on interaction strength. As a particular example we focus on a Lorentzian drive, which provides a clear signature of the minimal excitations known as Levitons. Here, we argue that inner-channel fractionalized excitations can be exploited to extract information about inter-channel interactions. We further confirm this idea by calculating the zero frequency noise due to the partitioning of these excitations at a quantum point contact and we propose a measurable quantity as a tool to directly probe electron-electron interactions and determine the so-called mixing angle of copropagating quantum Hall channels.

cond-mat.mes-hall↗

arXiv2017

Photoassisted shot noise spectroscopy at fractional filling factor

We study the photoassisted shot noise generated by a periodic voltage in the fractional quantum Hall regime. Fluctuations of the current are due to the presence of a quantum point contact operating in the weak backscattering regime. We show how to reconstruct the photoassisted absorption and emission probabilities by varying independently the dc and ac contributions to the voltage drive. This is made possible by the peculiar power-law behavior of the tunneling rates in the chiral Luttinger liquid theory, which allow to approximate the typical infinite sums of the photoassisted transport formalism in a simple and particularly convenient way.

cond-mat.mes-hall↗

arXiv2017

Tunable pseudogaps due to non-local coherent transport in voltage-biased three-terminal Josephson junctions

We investigate the proximity effect in junctions between $N=3$ superconductors under commensurate voltage bias. The bias is chosen to highlight the role of transport processes that exchange multiple Cooper pairs coherently between more than two superconductors. Such non-local processes can be studied in the dc response, where local transport processes do not contribute. We focus on the proximity-induced normal density of states that we investigate in a wide parameter space. We reveal the presence of deep and highly tunable pseudogaps and other rich structures. These are due to a static proximity effect that is absent for $N=2$ and is sensitive to an emergent superconducting phase associated to non-local coherent transport. In comparison with results for $N=2$, we find similarities in the signature peaks of multiple Andreev reflections. We discuss the effect of electron-hole decoherence and of various types of junction asymmetries. Our predictions can be investigated experimentally using tunneling spectroscopy.

cond-mat.mes-hall↗

arXiv2017

Minimal excitation states for heat transport in driven quantum Hall systems

We investigate minimal excitation states for heat transport into a fractional quantum Hall system driven out of equilibrium by means of time-periodic voltage pulses. A quantum point contact allows for tunneling of fractional quasi-particles between opposite edge states, thus acting as a beam splitter in the framework of the electron quantum optics. Excitations are then studied through heat and mixed noise generated by the random partitioning at the barrier. It is shown that levitons, the single-particle excitations of a filled Fermi sea recently observed in experiments, represent the cleanest states for heat transport, since excess heat and mixed shot noise both vanish only when Lorentzian voltage pulses carrying integer electric charge are applied to the conductor. This happens in the integer quantum Hall regime and for Laughlin fractional states as well, with no influence of fractional physics on the conditions for clean energy pulses. In addition, we demonstrate the robustness of such excitations to the overlap of Lorentzian wavepackets. Even though mixed and heat noise have nonlinear dependence on the voltage bias, and despite the non-integer power-law behavior arising from the fractional quantum Hall physics, an arbitrary superposition of levitons always generates minimal excitation states.

cond-mat.mes-hall↗

arXiv2014

Interactions and charge fractionalization in an electronic Hong-Ou-Mandel interferometer

We consider an electronic analog of the Hong-Ou-Mandel (HOM) interferometer, where two single electrons travel along opposite chiral edge states and collide at a Quantum Point Contact. Studying the current noise, we show that because of interactions between co-propagating edge states, the degree of indistinguishability between the two electron wavepackets is dramatically reduced, leading to reduced contrast for the HOM signal. This decoherence phenomenon strongly depends on the energy resolution of the packets. Insofar as interactions cause charge fractionalization, we show that charge and neutral modes interfere with each other, leading to satellite dips or peaks in the current noise. Our calculations explain recent experimental results [E. Bocquillon, et al., Science 339, 1054(2013)] where an electronic HOM signal with reduced contrast was observed.

cond-mat.mes-hall↗

arXiv2011

Many-body Correlation Effect on Mesoscopic Charge Relaxation

We investigate in a nonperturbative way the dynamics of a correlated quantum capacitor. We find that the many-body correlations do not disturb the universal low-frequency relaxation resistance per channel, $R_q(ω=0) = h/4e^2$ ensured by the Korringa-Shiba rule whereas the interpretation of the quantum capacitance $C_q$ in terms of the density of states fails when strong correlations are present. The AC resistance $R_q(ω)$ shows huge peaks (with values larger than $h/4e^2$) at $\hbarω\approx \pm Γ^*$, where $Γ^*$ is the renormalized level broadening. These peaks are merged to a single one at $ω=0$ when a finite Zeeman field is applied comparable to $Γ^*$. The observed features of $R_q$, being most evident in the Kondo regime, are attributed to the generation of particle-hole excitations in the contacts accomplished by spin-flip processes in the dot.

cond-mat.mes-hall↗

arXiv2010

Quantum phase transition of dynamical resistance in a mesoscopic capacitor

We study theoretically dynamic response of a mesoscopic capacitor, which consists of a quantum dot connected to an electron reservoir via a point contact and capacitively coupled to a gate voltage. A quantum Hall edge state with a filling factor nu is realized in a strong magnetic field applied perpendicular to the two-dimensional electron gas. We discuss a noise-driven quantum phase transition of the transport property of the edge state by taking into account an ohmic bath connected to the gate voltage. Without the noise, the charge relaxation for nu>1/2 is universally quantized at R_q=h/(2e^2), while for nu<1/2, the system undergoes the Kosterlitz-Thouless transtion, which drastically changes the nature of the dynamical resistance. The phase transition is facilitated by the noisy gate voltage, and we see that it can occur even for an integer quantum Hall edge at nu=1. When the dissipation by the noise is sufficiently small, the quantized value of R_q is shifted by the bath impedance.

cond-mat.mes-hall↗

arXiv2010

Poissonian tunneling through an extended impurity in the quantum Hall effect

We consider transport in the Poissonian regime between edge states in the quantum Hall effect. The backscattering potential is assumed to be arbitrary, as it allows for multiple tunneling paths. We show that the Schottky relation between the backscattering current and noise can be established in full generality: the Fano factor corresponds to the electron charge (the quasiparticle charge) in the integer (fractional) quantum Hall effect, as in the case of purely local tunneling. We derive an analytical expression for the backscattering current, which can be written as that of a local tunneling current, albeit with a renormalized tunneling amplitude which depends on the voltage bias. We apply our results to a separable tunneling amplitude which can represent an extended point contact in the integer or in the fractional quantum Hall effect. We show that the differential conductance of an extended quantum point contact is suppressed by the interference between tunneling paths, and it has an anomalous dependence with respect to the bias voltage.

cond-mat.mes-hall↗

arXiv2010

Dynamic response of a mesoscopic capacitor in the presence of strong electron interactions

We consider a one dimensional mesoscopic capacitor in the presence of strong electron interactions and compute its admittance in order to probe the universal nature of the relaxation resistance. We use a combination of perturbation theory, renormalization group arguments, and quantum Monte Carlo calculation to treat the whole parameter range of dot-lead coupling. The relaxation resistance is universal even in the presence of strong Coulomb blockade when the interactions in the wire are sufficiently weak. We predict and observe a quantum phase transition to an incoherent regime for a Luttinger parameter $K<1/2$. Results could be tested using a quantum dot coupled to an edge state in the fractional quantum Hall effect.

cond-mat.mes-hall↗

arXiv2010

Anomalous Hall effects and electron polarizability

A theory of the anomalous and spin Hall effects, based on the space distribution of the current densities, is presented. Spin-orbit coupling gives rise to a space separation of the mass centers, as well as a current density separation of the quasiparticle states having opposite group velocities. It is shown that this microscopic property is essential for existence of both Hall effects.

cond-mat.mes-hall↗

arXiv2010

Josephson effect through a multilevel dot near a singlet-triplet transition

We investigate the Josephson effect through a two-level quantum dot with an exchange coupling between two dot electrons. We compute the superconducting phase relationship and construct the phase diagram in the superconducting gap--exchange coupling plane in the regime of the singlet-triplet transition driven by the exchange coupling. In our study two configurations for the dot-lead coupling are considered: one where effectively only one channel couples to the dot, and the other where the two dot orbitals have opposite parities. Perturbative analysis in the weak-coupling limit reveals that the system experiences transitions from 0 to $π$ (negative critical current) behavior, depending on the parity of the orbitals and the spin correlation between dot electrons. The strong coupling regime is tackled with the numerical renormalization group method, which first characterizes the Kondo correlations due to the dot-lead coupling and the exchange coupling in the absence of superconductivity. In the presence of superconductivity, many-body correlations such as two-stage Kondo effect compete with the superconductivity and the comparison between the gap and the relevant Kondo temperature scales allows to predict a rich variety of phase diagrams for the ground state of the system and for the Josephson current. Numerical calculations predicts that our system can exhibit Kondo-driven 0-$π$-0 or $π$-0-$π$ double transitions and, more interestingly, that if proper conditions are met a Kondo-assisted $π$-junction can arise, which is contrary to a common belief that the Kondo effect opens a resonant level and makes the 0-junction. Our predictions could be probed experimentally for a buckminster fullerene sandwiched between two superconductors.

cond-mat.mes-hall↗

arXiv2010

Detection of finite frequency photo-assisted shot noise with a resonant circuit

Photo-assisted transport through a mesoscopic conductor occurs when an oscillatory (AC) voltage is superposed to the constant (DC) bias which is imposed on this conductor. Of particular interest is the photo assisted shot noise, which has been investigated theoretically and experimentally for several types of samples. For DC biased conductors, a detection scheme for finite frequency noise using a dissipative resonant circuit, which is inductively coupled to the mesoscopic device, was developped recently. We argue that the detection of the finite frequency photo-assisted shot noise can be achieved with the same setup, despite the fact that time translational invariance is absent here. We show that a measure of the photo-assisted shot noise can be obtained through the charge correlator associated with the resonant circuit, where the latter is averaged over the AC drive frequency. We test our predictions for a point contact placed in the fractional quantum Hall effect regime, for the case of weak backscattering. The Keldysh elements of the photo-assisted noise correlator are computed. For simple Laughlin fractions, the measured photo-assisted shot noise displays peaks at the frequency corresponding to the DC bias voltage, as well as satellite peaks separated by the AC drive frequency.

cond-mat.mes-hall↗

arXiv2009

Non-equilibrium supercurrent through a quantum dot: current harmonics and proximity effect due to a normal metal lead

We consider a Hamiltonian model for a quantum dot which is placed between two superconducting leads with a constant bias imposed between these leads. Using the non-equilibrium Keldysh technique, we focus on the subgap current, where it is known that multiple Andreev reflections (MAR) are responsible for charge transfer through the dot. Attention is put on the DC current and on the first harmonics of the supercurrent. Varying the energy and width of the resonant level on the dot, we first investigate a cross-over from a quantum dot regime to a quantum point contact regime when there is zero coupling to the normal probe. We then study the effect on the supercurrent of the normal probe which is attached to the dot. This normal probe is understood to lead to dephasing, or alternatively to induce reverse proximity effect. We describe the full crossover from zero dephasing to the incoherent case. We also compute the Josephson current in the presence of the normal lead, and find it in excellent agreement with the values of the non-equlibrium current extrapolated at zero voltage.

cond-mat.mes-hall↗

arXiv2009

Transport through a band insulator with Rashba spin-orbit coupling: metal-insulator transition and spin-filtering effects

We calculate the current-voltage characteristic of a one-dimensional band insulator with magnetic field and Rashba spin-orbit coupling which is connected to nonmagnetic leads. Without spin-orbit coupling we find a complete spin-filtering effect, meaning that the electric transport occurs in one spin channel only. For a large magnetic field which closes the band gap, we show that spin-orbit coupling leads to a transition from metallic to insulating behavior. The oscillations of the different spin-components of the current with the length of the transport channel are studied as well.

cond-mat.mes-hall↗

arXiv2008

Weak-field Hall effect and static polarizability of Bloch electrons

A theory of the weak field Hall effect of Bloch electrons based on the analysis of the forces acting on electrons is presented. It is argued that the electric current is composed of two contributions, that driven by the electric field along current flow and the non-dissipative contribution originated in demagnetization currents. The Hall resistance as a function of the electron concentration for the tight-binding model of a crystal with square lattice and body-centered cubic lattice is described in detail. For comparison the effect of strong magnetic fields is also discussed.

cond-mat.mes-hall↗

arXiv2008

Josephson Effect through an isotropic magnetic molecule

We investigate the Josephson effect through a molecular quantum dot magnet connected to superconducting leads. The molecule contains a magnetic atom, whose spin is assumed to be isotropic. It is coupled to the electron spin on the dot via exchange coupling. Using the numerical renormalization group method we calculate the Andreev levels and the supercurrent and examine intertwined effect of the exchange coupling, Kondo correlation, and superconductivity on the current. Exchange coupling typically suppresses the Kondo correlation so that the system undergoes a phase transition from 0 to $π$ state as the modulus of exchange coupling increases. Antiferromagnetic coupling is found to drive exotic transitions: the reentrance to the $π$ state for a small superconducting gap and the restoration of 0 state for large antiferromagnetic exchange coupling. We suggest that the asymmetric dependence of supercurrent on the exchange coupling could be used as to detect its sign in experiments.

cond-mat.mes-hall↗