Leggett mode controlled by light pulses

Giorgianni, F.; Cea, Tommaso; Vicario, C.; Hauri, Christoph P.; Withanage, Wenura K.; Xi, Xiaoxing; Benfatto, Lara

doi:10.1038/s41567-018-0385-4

Cited by 79 publications

(106 citation statements)

References 32 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…As a consequence, for broadband pulses the spectral components of δE probe (t pp ) are dominated by the characteristic frequency of the mode, ω osc = ω res , while for narrowband pulses δE probe (t pp ) oscillates at twice the pump frequency, ω osc = 2Ω pump , with an amplitude K(2Ω pump ) maximized when 2Ω pump = ω res . These expectations match rather well the observations reported so far in several SC systems [4][5][6][7][8] . From the theoretical point of view, establishing such a general paradigm provides also a scheme for further theoretical investigations aimed at linking the experimental observations to the properties of the underlying microscopic model.…”

supporting

confidence: 92%

“…The present work aims at filling in part this knowl- * mattia.udina@uniroma1.it † tommaso.cea@imdea.org ‡ lara.benfatto@roma1.infn.it edge gap by providing a general theoretical scheme to understand the origin of time-resolved oscillations observed in typical TH pump-THz/eV probe measurements. This experimental technique has been successfully applied in the last years to investigate the properties of both conventional superconducting (SC) compounds [4][5][6][7][8][9] , whose spectral gap ∆ lies in the THz region, and layered superconductors 10,11 with an interlayer Josephson plasma frequency again in the THz range. The general scheme consists in probing the effects of the intense THz pulse by measuring the pump-induced changes δE probe (t pp ) in the transmitted (for a thin film) or reflected (for a bulk crystal) probe field at a fixed observation time, as a function of the pump-probe delay t pp .…”

mentioning

confidence: 99%

See 1 more Smart Citation

Theory of coherent-oscillations generation in terahertz pump-probe spectroscopy: From phonons to electronic collective modes

2019

Self Cite

View full text Add to dashboard Cite

Time-resolved spectroscopies using intense THz pulses appear as a promising tool to address collective electronic excitations in condensed matter. In particular recent experiments showed the possibility to selectively excite collective modes emerging across a phase transition, as it is the case for superconducting and charge-density-wave (CDW) systems. One possible signature of these excitations is the emergence of coherent oscillations of the differential probe field in pump-probe protocols. While the analogy with the case of phonon modes suggests that the basic underlying mechanism should be a sum-frequency stimulated Raman process, a general theoretical scheme able to describe the experiments and to define the relevant optical quantity is still lacking. Here we provide this scheme by showing that coherent oscillations as a function of the pump-probe time delay can be linked to the convolution in the frequency domain between the squared pump field and a Raman-like non-linear optical kernel. This approach is applied and discussed in few paradigmatic examples: ordinary phonons in an insulator, and collective charge and Higgs fluctuations across a superconducting and a CDW transition. Our results not only account very well for the existing experimental data in a wide variety of systems, but they also offer an useful perspective to design future experiments in emerging materials.In the last decade, a significant advance in the investigation of complex systems has been gained thanks to the huge experimental progress in time-resolved spectroscopic techniques 1,2 . On very general grounds, the basic idea behind any pump-probe protocol is to first excite the system with a short and very intense electromagnetic pulse (pump), and then to monitor its relaxation towards equilibrium by using a secondary, weak pulse (probe) applied with a finite time delay with respect to the pump. This general protocol can then be implemented in several different ways, according to the nature of the spectroscopic measurement (angle-resolved photoemission, optical reflection or transmission, etc.) or to the wavelength of the pump/probe fields. However, in all cases one has to face with two phenomena which mark the difference with respect to ordinary equilibrium spectroscopies: (i) the use of an intense pulse triggers in general non-linear optical processes; (ii) the subsequent relaxation encodes by definition non-equilibrium phenomena on time scales which depend on the characteristics of the experiment and of the system under investigation. Due in part to these innovative aspects, many pump-probe protocols still lack a general theoretical framework able to connect the measured quantities to the material properties. More specifically, while Kubo linear-response theory 3 represents nowadays the standard theoretical tool needed to compute the optical response of any system to a weak external perturbation, an analogous protocol for timeresolved spectroscopies has not been established yet.The present work aims at filling in part this knowl- * mat...

show abstract

supporting

confidence: 92%

mentioning

confidence: 99%

Theory of coherent-oscillations generation in terahertz pump-probe spectroscopy: From phonons to electronic collective modes

2019

Self Cite

View full text Add to dashboard Cite

show abstract

“…An experimental observation of Leggett collective excitations is a challenging problem, because they, in general, have relatively small spectral weights or high decay rates. Leggett modes have been detected in a two-band superconductor MgB 2 using Raman [2] and tunneling [3] spectroscopy, and, recently, using intense terahertz lights pulses [4]. In the experimentally realized two-band 173 Yb cold atomic gases with OFR, Leggett collective excitations can be hardly resolved, because they are strongly damped in the experimentally achieved stable out-of-phase state [13].…”

Section: Discussionmentioning

confidence: 99%

“…Leggett modes were experimentally detected in multiband superconductors [2][3][4]. The two-band superfluidity and Leggett collective modes have been considered theoretically for superconducting MgB 2 [5] and for condensed Fermi gases in the BCS-BEC crossover [6,7].…”

Section: Introductionmentioning

confidence: 99%

Leggett collective excitations in a two-band Fermi superfluid at finite temperatures

2019

View full text Add to dashboard Cite

The Leggett collective excitations for a two-band Fermi gas with s-wave pairing and Josephson interband coupling in the BCS-BEC crossover at finite temperatures are investigated within the Gaussian pair fluctuation approach. Eigenfrequencies and damping factors for Leggett modes are determined in a nonperturbative way, using the analytic continuation of the fluctuation propagator through a branch cut in the complex frequency plane, as in Kurkjian et al (2019 Phys. Rev. Lett. 122 093403). The treatment is performed beyond the low-energy expansion, which is necessary when the collective excitation energy reaches the pair-breaking continuum edge. The results are applied in particular to cold atomic gases at the orbital Feshbach resonance and in a regime far from BEC, which can be relevant for future experiments.

show abstract

“…Finally, in addition to the Higgs mode, unconventional superconductors with reduced dimensionality and multi-band superconductors may host a much richer spectrum of collective excitations [142,157,158]. The first experiments, suggesting the observation of the collective oscillation of the relative phase between the order parameters in a two-band superconductor MgB 2 , the Leggett mode, have just been reported [159].…”

Section: Summary and Perspectivesmentioning

confidence: 99%

Non-equilibrium Phenomena in Superconductors Probed by Femtosecond Time-Domain Spectroscopy

Demšar

2020

J Low Temp Phys

View full text Add to dashboard Cite

Development of ultrafast lasers and non-linear optical techniques over the last two decades provides tools to access real-time dynamics of low energy excitations in superconductors. For example, time-resolved THz spectroscopy and time-and angular-resolved photoemission spectroscopy provide access to the real-time dynamics of the superconducting gap amplitude. Such studies enable determination of microscopic parameters like quasi-particle recombination rates, pair-breaking rates and electron-boson coupling constants. Recently, intense THz pulses have been used to probe the non-linear dynamics, including observation of collective modes. Moreover, using low frequency electromagnetic pulses, there are several reports of amplification of superconductivity in both conventional and unconventional superconductors. Starting with a brief historical overview of the pioneering work, where non-equilibrium phenomena in superconductors were investigated using quasi-continuous excitation, we review some of the insights that are provided by using real-time approaches. We focus on conventional BCS superconductors, whose ground state is reasonably well understood, and address similarities and open questions related to the corresponding studies in high-T c superconductors. arXiv:2003.11503v1 [cond-mat.supr-con]

show abstract

Leggett mode controlled by light pulses

Cited by 79 publications

References 32 publications

Theory of coherent-oscillations generation in terahertz pump-probe spectroscopy: From phonons to electronic collective modes

Theory of coherent-oscillations generation in terahertz pump-probe spectroscopy: From phonons to electronic collective modes

Leggett collective excitations in a two-band Fermi superfluid at finite temperatures

Non-equilibrium Phenomena in Superconductors Probed by Femtosecond Time-Domain Spectroscopy

Contact Info

Product

Resources

About