Revealing the high-energy electronic excitations underlying the onset of high-temperature superconductivity in cuprates.
TL;DR: The interplay between the many-body high-energy CuO2 excitations at 1.5 and 2 eV, and the onset of HTSC is reported, revealing an unconventional mechanism both below and above the optimal hole concentration required to attain the maximum critical temperature (Tc).
Abstract: In strongly correlated systems the electronic properties at the Fermi energy (EF) are intertwined with those at high-energy scales. One of the pivotal challenges in the field of high-temperature superconductivity (HTSC) is to understand whether and how the high-energy scale physics associated with Mott-like excitations (|E−EF|>1 eV) is involved in the condensate formation. Here, we report the interplay between the many-body high-energy CuO2 excitations at 1.5 and 2 eV, and the onset of HTSC. This is revealed by a novel optical pump-supercontinuum-probe technique that provides access to the dynamics of the dielectric function in Bi2Sr2Ca0.92Y0.08Cu2O8+δ over an extended energy range, after the photoinduced suppression of the superconducting pairing. These results unveil an unconventional mechanism at the base of HTSC both below and above the optimal hole concentration required to attain the maximum critical temperature (Tc).
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TL;DR: In the last two decades non-equilibrium spectroscopies have evolved from avant-garde studies to crucial tools for expanding our understanding of the physics of strongly correlated materials as mentioned in this paper.
Abstract: In the last two decades non-equilibrium spectroscopies have evolved from avant-garde studies to crucial tools for expanding our understanding of the physics of strongly correlated materials. The possibility of obtaining simultaneously spectroscopic and temporal information has led to insights that are complementary to (and in several cases beyond) those attainable by studying the matter at equilibrium. From this perspective, multiple phase transitions and new orders arising from competing interactions are benchmark examples where the interplay among electrons, lattice and spin dynamics can be disentangled because of the different timescales that characterize the recovery of the initial ground state. For example, the nature of the broken-symmetry phases and of the bosonic excitations that mediate the electronic interactions, eventually leading to superconductivity or other exotic states, can be revealed by observing the sub-picosecond dynamics of impulsively excited states. Furthermore, recent experimental...
306 citations
TL;DR: In this article, a review of the most recent achievements in the experimental and theoretical studies of the non-equilibrium electronic, optical, structural and magnetic properties of correlated materials is presented.
Abstract: In the last two decades, non-equilibrium spectroscopies have evolved from avant-garde studies to crucial tools for expanding our understanding of the physics of strongly correlated materials. The possibility of obtaining simultaneously spectroscopic and temporal information has led to insights that are complementary to (and in several cases beyond) those attainable by studying the matter at equilibrium. Multiple phase transitions and new orders arising from competing interactions are benchmark examples where the interplay among electrons, lattice, and spin dynamics can be disentangled because of the different timescales that characterize the recovery of the initial ground state. The nature of the broken-symmetry phases and of the bosonic excitations that mediate the electronic interactions, eventually leading to superconductivity or other exotic states, can be revealed by observing the sub-picosecond dynamics of impulsively excited states. Recent experimental developments have made possible to monitor the time-evolution of both the single-particle and collective excitations under extreme conditions, such as those arising from strong and selective photo-stimulation.
Here, we review the most recent achievements in the experimental and theoretical studies of the non-equilibrium electronic, optical, structural and magnetic properties of correlated materials. The focus will be mainly on the prototypical case of correlated oxides that exhibit unconventional superconductivity or other exotic phases, even though the discussion will extend also to other topical systems. The necessity of extending the actual experimental capabilities and the numerical and analytic tools to microscopically treat the non-equilibrium phenomena beyond the simple phenomenological approaches represents one of the most challenging new frontier in physics.
243 citations
TL;DR: Time-resolved optical spectroscopy of an optimally doped cuprate is used to show that the temporal evolution of the reflectivity is consistent with the electronic contribution being dominant and is able to account for the high Tc by itself.
Abstract: Unveiling the nature of the bosonic excitations that mediate the formation of Cooper pairs is a key issue for understanding unconventional superconductivity. A fundamental step toward this goal would be to identify the relative weight of the electronic and phononic contributions to the overall frequency (Ω)-dependent bosonic function, Π(Ω). We performed optical spectroscopy on Bi(2)Sr(2)Ca(0.92)Y(0.08)Cu(2)O(8+δ) crystals with simultaneous time and frequency resolution; this technique allowed us to disentangle the electronic and phononic contributions by their different temporal evolution. The spectral distribution of the electronic excitations and the strength of their interaction with fermionic quasiparticles fully account for the high critical temperature of the superconducting phase transition.
163 citations
TL;DR: In this article, a review of recent developments in this emerging field is presented and examples include the cuprates, manganites, and vanadates, as well as other transition metal oxides.
Abstract: Advances in the synthesis, growth, and characterization of complex transition metal oxides coupled with new experimental techniques in ultrafast optical spectroscopy have ushered in an exciting era of dynamics and control in these materials. Experiments utilizing femtosecond optical pulses can initiate and probe dynamics of the spin, lattice, orbital, and charge degrees of freedom. Major goals include (a) determining how interaction and competition between the relevant degrees of freedom determine macroscopic functionality in transition metal oxides (TMOs) and (b) searching for hidden phases in TMOs by controlling dynamic trajectories in a complex and pliable energy landscape. Advances in creating intense pulses from the far-IR spectrum through the visible spectrum enable mode-selective excitation to facilitate exploration of these possibilities. This review covers recent developments in this emerging field and presents examples that include the cuprates, manganites, and vanadates.
158 citations
TL;DR: Subpicosecond laser pulses can selectively excite modes of strongly correlated electron systems and controllably push materials from one ordered phase to another as discussed by the authors, and can be used to control the behavior of electron systems.
Abstract: Subpicosecond laser pulses can selectively excite modes of strongly correlated electron systems and controllably push materials from one ordered phase to another.
134 citations
References
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Book•
01 Jan 1975
TL;DR: In this article, a revised version of the book has been published to incorporate the many new developments in superconductivity, including new topics on high temperature superconductors and nonequilibrium superconductivities.
Abstract: Appropriate for intermediate or advanced courses in superconductivity, this edition has been revised to incorporate the many new developments in superconductivity. Expanded topic coverage includes new chapters on high temperature superconductors and nonequilibrium superconductivity.
7,800 citations
TL;DR: Although assuming that doping creates holes primarily on oxygen sites, this work derives explicitly a single-band effective Hamiltonian for the high-${T}_{c}$ Cu-oxide superconductors.
Abstract: Although assuming that doping creates holes primarily on oxygen sites, we derive explicitly a single-band effective Hamiltonian for the high-${T}_{c}$ Cu-oxide superconductors. Cu-O hybridization strongly binds a hole on each square of O atoms to the central ${\mathrm{Cu}}^{2+}$ ion to form a local singlet. This moves through the lattice in a similar way as a hole in the single-band effective Hamiltonian of the strongly interacting Hubbard model.
2,350 citations
"Revealing the high-energy electroni..." refers background in this paper
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TL;DR: A new theory is presented for describing band gaps and electronic structures of transition-metal compounds and both the metallic sulfides and insulating oxides and halides occur in a quite natural manner.
Abstract: A new theory is presented for describing band gaps and electronic structures of transition-metal compounds. A theoretical phase diagram is presented in which both the metallic sulfides and insulating oxides and halides occur in a quite natural manner.
2,190 citations
01 Jan 2011
TL;DR: Onnes as discussed by the authors showed that the conductivity of pure metals at low temperatures increases by several orders of magnitude at temperatures below 4.18 K, and this discovery of superconductivity remained a mystery for more than 40 years.
Abstract: We have seen how the conductivity of a metal is limited by collisions, which determine the electron mean free path. After a collision, an electron completely loses all memory of its quantum state as specified by its quasi-momentum k. It is thus impossible to follow a Bloch state over any distance much greater than the mean free path. To understand the microscopic origin of these collisions, one had to measure the conductivity of very pure metals at low temperatures. This was made possible by the work of the physicist Kammerlingh Onnes, who specialised in the liquefaction of gases and opened the way to the use of cryogenic fluids. In 1911, he succeeded in liquefying 4He, at a temperature of 4.2 K. He then suggested using the low temperatures created in this way to study the low temperature conductivity of pure metals. Quite unexpectedly, he discovered that the conductivity of mercury increased by several orders of magnitude at temperatures below 4.18 K. This discovery of superconductivity remained a mystery for more than 40 years. With hindsight, it is clear that the prerequisites of quantum mechanics had not yet been established. Of course, this did not prevent the physicists of the first half of the twentieth century from gradually getting a hold on the fundamental manifestations of this phenomenon through ideas based entirely on experimental observations.
1,234 citations
TL;DR: In this paper, annealing results for several Tl-superconductors in the series Tlm(Ba, Sr)2Can−1CunO2n+m+2+δ, for both m=1 and 2, revealing two general results for this class of Bi or TI superconductors: (1) effects on Tc due to labile oxygen occur for all m=2 compounds but are absent in m = 1 compounds with Sr.
Abstract: We have previously shown that Tc for Bi2 (Sr, Ca)n+1CunO2n+4+δ (n=1, 2 and 3) varies with oxygen stoichiometry δ determined by annealing in a variety of oxygen partial pressures and temperatures. Annealing results are now also presented for several Tl-superconductors in the series Tlm(Ba, Sr)2Can−1CunO2n+m+2+δ, for both m=1 and 2, revealing two general results for this class of Bi or TI superconductors: (1) effects on Tc due to labile oxygen occur for all m=2 compounds but are absent in m = 1 compounds with Sr. m=1 compounds with Ba do have variable oxygen but the effects on the c-axis are the opposite to m=2 compounds. This suggests for the latter that the labile oxygen resides in interstitial sites within the Bi2O2 or Tl2O2 bi layers; (2) the hole concentration per Cu decreases in progressing from n = 1 to 2 to 3 in either class so that the parent n = 3 and n = 2 compounds lie respectively on the low- and high-hole concentration sides of the peak in Tc while the n = 1 compounds extend out into the non-superconducting domain at very high hole concentration.
712 citations