Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:1309.7318 · Physical Review B

Signatures of nonadiabatic BCS state dynamics in pump-probe conductivity

H. Krull, Dirk Manske, Götz Silvester Uhrig, Andreas P. Schnyder

Published Jul 25, 2014• 69 citations
arXivHTMLPDF

Abstract

We theoretically study the pump-probe response of nonequilibrium BCS superconductors coupled to optical phonons. For ultrashort pump pulses a nonadiabatic regime emerges, which is characterized by oscillations of the superconducting order parameter as well as by the generation of coherent phonons. Using the density-matrix formalism, we compute the pump-probe response in the nonadiabatic regime of the coupled Bogoliubov quasiparticle-phonon system and determine the signatures of the order parameter and the phonon oscillations in the pump-probe conductivity. We find that the nonadiabatic dynamics of the BCS superconductor reflects itself in oscillations of the pump-probe response as functions of delay time $\ensuremath{\delta}t$ between pump and probe pulses. We argue that from the analysis of this oscillatory behavior both frequency and decay time of the algebraically decaying order-parameter oscillations can be inferred. Similarly, the coherent phonons are evidenced in the pump-probe conductivity by oscillations with the frequency of the phonons. Remarkably, we find that the oscillatory response in the pump-probe conductivity is resonantly enhanced when the frequency of the order-parameter oscillations is tuned to the phonon energy.

DOI
10.1103/physrevb.90.014515

Related papers

Coherent control of the gap dynamics of BCS superconductors in the nonadiabatic regime

Thomas Papenkort, T. Kühn, V. M. Axt

By exciting a BCS superconductor with ultrashort pulses in the frequency range of the superconducting gap a nonadiabatic regime can be reached. In this regime the modulus of the order parameter oscillates in time. Although its average value can be identified with the gap in the absorption spectrum, the oscillation itself remains invisible in pump-probe spectra. In this Brief Report we demonstrate that by employing a coherent control-type scheme of excitation by two phase-locked pump pulses this oscillation can be unveiled in the probe spectrum. We find that the reaction of the superconductor to a second pump pulse depends strongly on its instantaneous state at the time of the impact of the second pulse. Based on numerical calculations performed on the mean-field level it is shown that by varying the delay time between the two pump pulses the transient oscillation of the order parameter can be transformed into an oscillation of its long-time value, which shows up in the absorption spectrum of a subsequent weak probe pulse as an oscillation of the gap when plotted as a function of the delay time.

Physical Review B•Oct 9, 2008•59 citations

Coherent dynamics and pump-probe spectra of BCS superconductors

Thomas Papenkort, V. M. Axt, T. Kühn

The density matrix formalism is employed to calculate pump-probe spectra of BCS superconductors in the coherent regime. Two dynamical regimes, one adiabatic and one nonadiabatic, can be clearly distinguished. In the adiabatic regime, the modulus of the BCS order parameter can be identified with half the gap in the probe spectra. In the nonadiabatic regime, the order parameter oscillates in real time, whereas the gap observed in the spectra reflects its temporal average. The transition between these regimes is accompanied by a qualitative change of the intensity dependence of the dynamical gap renormalization. Furthermore, a hole-burning effect occurs if the spectral shape of the pump pulse is sufficiently sharp. A probe pulse preceding the pump pulse leads to spectral oscillations, and both the gap before and after the pump pulse are visible in the probe spectra.

Physical Review B•Dec 21, 2007•111 citations

Quantum Dynamics of the Hubbard-Holstein Model in Equilibrium and Nonequilibrium: Application to Pump-Probe Phenomena

G. De Filippis, V. Cataudella, Elizabeth Nowadnick +3 more

The spectral response and physical features of the 2D Hubbard-Holstein model are calculated both in equilibrium at zero and low chemical dopings, and after an ultrashort powerful light pulse, in undoped systems. At equilibrium and at strong charge-lattice couplings, the optical conductivity reveals a three-peak structure in agreement with experimental observations. After an ultrashort pulse and at nonzero electron-phonon interaction, phonon and spin subsystems oscillate with the phonon period T(ph)≈80 fs. The decay time of the phonon oscillations is about 150-200 fs, similar to the relaxation time of the charge system. We propose a criterion for observing these oscillations in high T(c) compounds: the time span of the pump light pulse τ(pump) has to be shorter than the phonon oscillation period T(ph).

arXiv:1206.0110•Physical Review Letters•Oct 23, 2012•81 citations

Nonequilibrium dynamics from BCS to the bosonic limit

G. Seibold, J. Lorenzana

Within the time-dependent Gutzwiller approximation applied to the negative-$U$ Hubbard model, we investigate the dynamics of a superconductor after an interaction quench for different values of the final interaction from weak to strong coupling. The equilibrium BCS-BEC crossover becomes a sharp transition in the out-of-equilibrium dynamics between weak- and strong-coupling dynamical phases. Two different frequencies (${\mathrm{\ensuremath{\Omega}}}_{J}<{\mathrm{\ensuremath{\Omega}}}_{U}$) dominate the order parameter dynamics. In the weak coupling phase, ${\mathrm{\ensuremath{\Omega}}}_{J}$ follows twice the asymptotic average value of the gap (${\mathrm{\ensuremath{\Omega}}}_{J}\ensuremath{\approx}2{\mathrm{\ensuremath{\Delta}}}_{\ensuremath{\infty}}$) and ${\mathrm{\ensuremath{\Omega}}}_{U}$ is much larger but hardy visible in the anomalous density. At long times the BCS dynamics is recovered but surprisingly differences remain during the transient phase. In the strong coupling phase, the dynamics decouples from the asymptotic value of the order parameter except at exactly half filling and close to the dynamical transition where ${\mathrm{\ensuremath{\Omega}}}_{U}\ensuremath{\approx}2{\mathrm{\ensuremath{\Delta}}}_{\ensuremath{\infty}}$. The out-of-equilibrium transient spectral density and optical conductivity are presented and discussed in relation to pump probe experiments. Both ${\mathrm{\ensuremath{\Omega}}}_{J}$ and ${\mathrm{\ensuremath{\Omega}}}_{U}$ give rise to a complex structure of self-driven slow Rabi oscillations which are visible in the nonequilibrium optical conductivity where also sidebands appear due to the modulation of the double occupancy by superconducting amplitude oscillations. Analogous results apply to CDW and SDW systems. Our results show that in systems with long coherence times, pump-probe experiments allow us to characterize the regime (BCS vs preformed pairs) through very specific out-of-equilibrium fingerprints.

arXiv:2004.02454•Physical review. B./Physical review. B•Oct 5, 2020•12 citations

Theory of ultrafast nonequilibrium dynamics in d -wave superconductors

Julia Unterhinninghofen, Dirk Manske, A. Knorr

We use density-matrix theory to calculate the ultrafast dynamics of unconventional superconductors from a microscopic viewpoint. We calculate the time evolution of the optical conductivity as well as pump-probe spectra for a $d$-wave order parameter. Three regimes can be distinguished in the spectra. The Drude response at low photon energies is the only one of those which has been experimentally measured so far. At higher energies, we predict two more regimes: the pair-breaking peak, which is reduced as Cooper pairs are broken up by the exciting pulse, and a suppression above the pair-breaking peak due to nonequilibrium quasiparticles. Furthermore, we consider the influence of the electron-phonon coupling and derive rate equations that have been widely used so far.

arXiv:0707.1567•Physical Review B•May 22, 2008•34 citations

Higgs oscillations in time-resolved optical conductivity

Ankit Kumar, Alexander F. Kemper

Driving superconductors out of equilibrium is a promising avenue to study their equilibrium properties as well as to control the superconducting state. Nonequilibrium superconductors are often studied using time-resolved optical conductivity measurements. Thus, the characterization of a superconducting state in a pump driven nonequilibrium state requires careful attention in the time domain. We calculate the time-resolved optical conductivity of a pumped superconducting state using a nonequilibrium Keldysh approach. Through functional derivation, the optical conductivity is obtained with full vertex corrections and used to characterize the transient superconducting state. The transient optical conductivity shows the suppression of the superconducting order parameter in the time domain. The subsequent recovery of the order parameter exhibits oscillatory behavior that corresponds to the Higgs amplitude mode, and may be seen in several parts of the spectrum.

arXiv:1902.09549•Physical review. B./Physical review. B•Nov 21, 2019•19 citations
We theoretically study the pump-probe response of nonequilibrium BCS superconductors coupled to optical phonons. For ultrashort pump pulses a nonadiabatic regime emerges, which is characterized by oscillations of the superconducting order parameter as well as by the generation of coherent phonons. Using the density-matrix formalism, we compute the pump-probe response in the nonadiabatic regime of the coupled Bogoliubov quasiparticle-phonon system and determine the signatures of the order parameter and the phonon oscillations in the pump-probe conductivity. We find that the nonadiabatic dynamics of the BCS superconductor reflects itself in oscillations of the pump-probe response as functions of delay time \ensuremathδt\ensuremath{\delta}t\ensuremathδt between pump and probe pulses. We argue that from the analysis of this oscillatory behavior both frequency and decay time of the algebraically decaying order-parameter oscillations can be inferred. Similarly, the coherent phonons are evidenced in the pump-probe conductivity by oscillations with the frequency of the phonons. Remarkably, we find that the oscillatory response in the pump-probe conductivity is resonantly enhanced when the frequency of the order-parameter oscillations is tuned to the phonon energy.
By exciting a BCS superconductor with ultrashort pulses in the frequency range of the superconducting gap a nonadiabatic regime can be reached. In this regime the modulus of the order parameter oscillates in time. Although its average value can be identified with the gap in the absorption spectrum, the oscillation itself remains invisible in pump-probe spectra. In this Brief Report we demonstrate that by employing a coherent control-type scheme of excitation by two phase-locked pump pulses this oscillation can be unveiled in the probe spectrum. We find that the reaction of the superconductor to a second pump pulse depends strongly on its instantaneous state at the time of the impact of the second pulse. Based on numerical calculations performed on the mean-field level it is shown that by varying the delay time between the two pump pulses the transient oscillation of the order parameter can be transformed into an oscillation of its long-time value, which shows up in the absorption spectrum of a subsequent weak probe pulse as an oscillation of the gap when plotted as a function of the delay time.
The density matrix formalism is employed to calculate pump-probe spectra of BCS superconductors in the coherent regime. Two dynamical regimes, one adiabatic and one nonadiabatic, can be clearly distinguished. In the adiabatic regime, the modulus of the BCS order parameter can be identified with half the gap in the probe spectra. In the nonadiabatic regime, the order parameter oscillates in real time, whereas the gap observed in the spectra reflects its temporal average. The transition between these regimes is accompanied by a qualitative change of the intensity dependence of the dynamical gap renormalization. Furthermore, a hole-burning effect occurs if the spectral shape of the pump pulse is sufficiently sharp. A probe pulse preceding the pump pulse leads to spectral oscillations, and both the gap before and after the pump pulse are visible in the probe spectra.
The spectral response and physical features of the 2D Hubbard-Holstein model are calculated both in equilibrium at zero and low chemical dopings, and after an ultrashort powerful light pulse, in undoped systems. At equilibrium and at strong charge-lattice couplings, the optical conductivity reveals a three-peak structure in agreement with experimental observations. After an ultrashort pulse and at nonzero electron-phonon interaction, phonon and spin subsystems oscillate with the phonon period T(ph)≈80 fs. The decay time of the phonon oscillations is about 150-200 fs, similar to the relaxation time of the charge system. We propose a criterion for observing these oscillations in high T(c) compounds: the time span of the pump light pulse τ(pump) has to be shorter than the phonon oscillation period T(ph).
Within the time-dependent Gutzwiller approximation applied to the negative-UUU Hubbard model, we investigate the dynamics of a superconductor after an interaction quench for different values of the final interaction from weak to strong coupling. The equilibrium BCS-BEC crossover becomes a sharp transition in the out-of-equilibrium dynamics between weak- and strong-coupling dynamical phases. Two different frequencies (${\mathrm{\ensuremath{\Omega}}}_{J}<{\mathrm{\ensuremath{\Omega}}}_{U}$) dominate the order parameter dynamics. In the weak coupling phase, ${\mathrm{\ensuremath{\Omega}}}_{J}$ follows twice the asymptotic average value of the gap (${\mathrm{\ensuremath{\Omega}}}_{J}\ensuremath{\approx}2{\mathrm{\ensuremath{\Delta}}}_{\ensuremath{\infty}}$) and ${\mathrm{\ensuremath{\Omega}}}_{U}$ is much larger but hardy visible in the anomalous density. At long times the BCS dynamics is recovered but surprisingly differences remain during the transient phase. In the strong coupling phase, the dynamics decouples from the asymptotic value of the order parameter except at exactly half filling and close to the dynamical transition where ${\mathrm{\ensuremath{\Omega}}}_{U}\ensuremath{\approx}2{\mathrm{\ensuremath{\Delta}}}_{\ensuremath{\infty}}$. The out-of-equilibrium transient spectral density and optical conductivity are presented and discussed in relation to pump probe experiments. Both ${\mathrm{\ensuremath{\Omega}}}_{J}$ and ${\mathrm{\ensuremath{\Omega}}}_{U}$ give rise to a complex structure of self-driven slow Rabi oscillations which are visible in the nonequilibrium optical conductivity where also sidebands appear due to the modulation of the double occupancy by superconducting amplitude oscillations. Analogous results apply to CDW and SDW systems. Our results show that in systems with long coherence times, pump-probe experiments allow us to characterize the regime (BCS vs preformed pairs) through very specific out-of-equilibrium fingerprints.
We use density-matrix theory to calculate the ultrafast dynamics of unconventional superconductors from a microscopic viewpoint. We calculate the time evolution of the optical conductivity as well as pump-probe spectra for a ddd-wave order parameter. Three regimes can be distinguished in the spectra. The Drude response at low photon energies is the only one of those which has been experimentally measured so far. At higher energies, we predict two more regimes: the pair-breaking peak, which is reduced as Cooper pairs are broken up by the exciting pulse, and a suppression above the pair-breaking peak due to nonequilibrium quasiparticles. Furthermore, we consider the influence of the electron-phonon coupling and derive rate equations that have been widely used so far.
Driving superconductors out of equilibrium is a promising avenue to study their equilibrium properties as well as to control the superconducting state. Nonequilibrium superconductors are often studied using time-resolved optical conductivity measurements. Thus, the characterization of a superconducting state in a pump driven nonequilibrium state requires careful attention in the time domain. We calculate the time-resolved optical conductivity of a pumped superconducting state using a nonequilibrium Keldysh approach. Through functional derivation, the optical conductivity is obtained with full vertex corrections and used to characterize the transient superconducting state. The transient optical conductivity shows the suppression of the superconducting order parameter in the time domain. The subsequent recovery of the order parameter exhibits oscillatory behavior that corresponds to the Higgs amplitude mode, and may be seen in several parts of the spectrum.