Ultrafast dynamics in the presence of antiferromagnetic correlations in electron-doped cuprate La2−xCexCuO4±δ

Abstract

We used femtosecond optical pump-probe spectroscopy to study the photoinduced change in reflectivity of thin films of the electron-doped cuprate La 2−x Ce x CuO 4 (LCCO) with dopings of x = 0.08 (underdoped) and x = 0.11 (optimally doped). Above T c , we observe fluence-dependent relaxation rates that begin at a temperature similar to the one where transport measurements first show signatures of antiferromagnetic correlations. Upon suppressing superconductivity with a magnetic field, it is found that the fluence and temperature dependence of relaxation rates are consistent with bimolecular recombination of electrons and holes across a gap (2 AF ) originating from antiferromagnetic correlations which comprise the pseudogap in electron-doped cuprates. This can be used to learn about coupling between electrons and high-energy (ω > 2 AF ) excitations in these compounds and set limits on the time scales on which antiferromagnetic correlations are static.

Bosonic excitations and electron pairing in an electron-doped cuprate superconductor

“…This type of signal corresponds to the dark blue region in Fig. 1b, and seems to be quite common in cuprates [17][18][19] . Due to similarities between the four samples, all detailed analyses below are for data taken on sample II except where noted.…”

“…Here, low pump fluence is crucial as it helps yield fluence-independent parameters and enables us to extract accurate physical information using the effective temperature model described below. Because, at high pump fluences, Γ below T * will obviously deviate from this power law 19 . In addition, we surprisingly notice that T c almost increases linearly with increasing T * for the investigated samples (see Fig.…”

“…Under non-equilibrium conditions, these bosonic excitations display distinct relaxation dynamics because of their different couplings to the charge carriers and may thereby be potentially disentangled. This technique has been extensively utilized in studying the SC gap, pseudogap and competing orders on high-T c superconductors [14][15][16][17][18][19] , but its application on unveiling the entangled bosonic excitations and their temperature evolution remains elusive 13,20,21 .…”

Controlling competing orders via nonequilibrium acoustic phonons: Emergence of anisotropic effective electronic temperature

“…Recent advances in ultrafast pump-and-probe techniques, however, opened a new avenue to explore and control these competing electronic states, as they generally undergo different relaxation processes to return to equilibrium [5][6][7][8][9][10][11][12][13]. Importantly, by taking the system out of equilibrium, its parameters change on ultrafast time scales, which can result in transient electronic states with no equilibrium counterpart.…”

Disorder-sensitive pump-probe measurements onNd1.83Ce0.17CuO4±δfilms

“…Guided by the idea that defects not only affect the spectrum of excitations of the pristine system, but they can even induce/foster new excitations in the system in connection to their degree of positional disorder, we have performed time-resolved reflectivity (TRR) pump-probe experiments on three films of N d 1.83 Ce 0.17 CuO 4±δ with substantially different in-plane transport properties induced by different fabrication procedures and/or ex-situ thermal treatments with respect to oxygen content and disorder. Our choice of the TRR technique was dictated by the well-proven capability of pump-probe techniques to reveal the presence of various kinds of excitations in a system identifying their different relaxation dynamics [23][24][25][26][27][28][29][30][31][32][33][34] . A new excitation manifested as additional relaxation channel proving that it is possible to turn a TRR measurement, although indirectly, into a disorder-sensitive probe.…”