Probing optically silent superfluid stripes in cuprates

Rajasekaran, Srivats; Okamoto, Junichi; Mathey, Ludwig; Fechner, Michael; Thampy, Vivek; Gu, Genda; Cavalleri, Andrea

doi:10.1126/science.aan3438

Cited by 84 publications

(79 citation statements)

References 32 publications

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“…(1) the differential field δE probe (t pp ) shows marked oscillations when entering in the SC state [4][5][6][7][8] . At the same time, below the SC critical temperature T c a marked THG has been observed 6,11,31 , which has been also ascribed to SC collective modes 6,8,[32][33][34][35][36][37][38][39] . For the case of conventional superconductors, like thin films of NbN, both pump-probe protocols and THG measurements show that the relevant frequency is twice the value of the SC gap ∆.…”

Section: Pump-probe Spectroscopy Of Superconducting Modesmentioning

confidence: 89%

“…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 .…”

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confidence: 99%

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

2019

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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...

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Section: Pump-probe Spectroscopy Of Superconducting Modesmentioning

confidence: 89%

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confidence: 99%

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

2019

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“…The first value should now be familiar to the reader, coinciding with features in both the c-axis optical conductivity and giant phonon anomaly measurements on type B cuprates. Could this constitute an example where at high temperatures one probes properties of a close-in-energy type B ground state, while at low-temperatures that system (Tranquada et al 1995) c-axis transport (Li et al 2007) Inelastic X-ray scattering (Miao et al 2017 La 2−x Sr x CuO 4 × Nuclear magnetic resonance (Imai et al 2017) X-ray diffraction (Thampy et al 2014, Croft et al 2014 Non-linear optical response (Rajasekaran et al 2018) Hourglass magnon spectrum (Chan et al 2016)…”

Section: Methodsmentioning

confidence: 99%

Anomalies in the pseudogap phase of the cuprates: competing ground states and the role of umklapp scattering

et al. 2019

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Over the past two decades, advances in computational algorithms have revealed a curious property of the two-dimensional Hubbard model (and related theories) with hole doping: the presence of close-in-energy competing ground states that display very different physical properties. On the one hand, there is a complicated state exhibiting intertwined spin, charge, and pair density wave orders. We call this 'type A'. On the other hand, there is a uniform d-wave superconducting state that we denote as 'type B'. We advocate, with the support of both microscopic theoretical calculations and experimental data, dividing the high-temperature cuprate superconductors into two corresponding families, whose properties reflect either the type A or type B ground states at low temperatures. We review the anomalous properties of the pseudogap phase that led us to this picture, and present a modern perspective on the role that umklapp scattering plays in these phenomena in the type B materials. This reflects a consistent framework that has emerged over the last decade, in which Mott correlations at weak coupling drive the formation of the pseudogap. We discuss this development, recent theory and experiments, and open issues. * If one did not refermionise the spin sector, the non-linear interaction term within the bosonic theory reads −4g a =b cos Θ a cos Θ b , which is suggestive of a high symmetry. * This is easy to see in the purely bosonic language, as the interaction term −4g cos Θ sf cos Θ f at strong coupling pins the bosons to (Θ sf , Θ f ) = (2mπ, 2nπ or (Θ sf , Θ f ) = [2m + 1]π, [2n + 1]π with n, m ∈ Z. * Interestingly, recent gauge theory calculations that are proposed to apply to the pseudogap phase of the cuprates find such a deformation of the Fermi surface. See figure 7(a) of (Sachdev et al. 2018).

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“…This issue can be resolved by invoking a partner competitor like p-h pairs, which reduces the temperature window of superconducting fluctuations near T c . 95 Furthermore, recent observation of preformed p-p pairs up to T * in pump probe experiments [96][97][98] revived the idea of fluctuating preformed pairs.…”

Section: Connection With Theories On Preformed Cooper Pairsmentioning

confidence: 99%

Fractionalized pair density wave in the pseudogap phase of cuprate superconductors

et al. 2019

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The mysterious pseudo-gap (PG) phase of cuprate superconductors has been the subject of intense investigation over the last thirty years, but without a clear agreement about its origin. Owing to a recent observation in Raman spectroscopy, of a precursor in the charge channel, on top of the well known fact of a precursor in the superconducting channel, we present here a novel idea: the PG is formed through a Higgs mechanism, where two kinds of preformed pairs, in the particle-particle and particle-hole channels, become entangled through a freezing of their global phase. Remarkably, this entanglement is equivalent to fractionalizing a bond Cooper pair density wave (PDW) into its elementary parts; the particle-hole pair, giving rise to both density modulations and current modulations, and the particle-particle counterpart, leading to the formation of Cooper pairs. From this perspective, the "fractionalized PDW" becomes the central object around the formation of the pseudo-gap. The "locking" of phases between the charge and superconducting modes gives a unique explanation for the unusual global phase coherence of short-range charge modulations, observed below Tc on phase sensitive scanning tunneling microscopy (STM). A simple microscopic model enables us to estimate the mean-field values of the precursor gaps in each channel and the PG energy scale, and to compare them to the values observed in Raman scattering spectroscopy. We also discuss the possibility of a multiplicity of orders in the PG phase and give an overview of the phase diagram. arXiv:1906.01633v2 [cond-mat.supr-con]

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Probing optically silent superfluid stripes in cuprates

Cited by 84 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

Anomalies in the pseudogap phase of the cuprates: competing ground states and the role of umklapp scattering

Fractionalized pair density wave in the pseudogap phase of cuprate superconductors

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