Quantum spin correlations through the superconducting-to-normal phase transition in electron-doped superconducting Pr _0.88 LaCe _0.12 CuO _4-δ

Abstract

The quantum spin fluctuations of the S ‫؍‬ 1/2 Cu ions are important in determining the physical properties of high-transition-temperature (high Tc) copper oxide superconductors, but their possible role in the electron pairing of superconductivity remains an open question. The principal feature of the spin fluctuations in optimally doped high-Tc superconductors is a well defined magnetic resonance whose energy (ER) tracks Tc (as the composition is varied) and whose intensity develops like an order parameter in the superconducting state. We show that the suppression of superconductivity and its associated condensation energy by a magnetic field in the electron-doped high-Tc superconductor Pr0.88LaCe0.12CuO4-␦ (Tc ‫؍‬ 24 K), is accompanied by the complete suppression of the resonance and the concomitant emergence of static antiferromagnetic order. Our results demonstrate that the resonance is intimately related to the superconducting condensation energy, and thus suggest that it plays a role in the electron pairing and superconductivity.spin fluctuations ͉ strongly correlated electron materials ͉ superconductivity T he parent compounds of the high-T c copper oxide superconductors are Mott insulators characterized by a very strong antiferromagnetic (AF) exchange in the CuO 2 planes and static long-range AF order. Doping holes or electrons into the CuO 2 planes suppresses the static AF order and induces a superconducting phase, with energetic short-range AF spin fluctuations that are peaked around the AF wave vector Q ϭ (1/2, 1/2) in the reciprocal space of the two-dimensional CuO 2 planes ( Fig. 1a) (1). Understanding the relationship between the insulating AF and superconducting phases remains a key challenge in the search for a microscopic mechanism of high-T c superconductivity (2, 3). For optimally hole-and electron-doped high-T c superconductors, the most prominent new feature in the spin fluctuation spectrum is a collective magnetic excitation known as the resonance mode, which also is centered at Q ϭ (1/2, 1/2) and whose characteristic energy (E R ) is proportional to T c (4-8). The resonance only appears below the superconducting transition temperature in these optimally doped systems and is fundamentally linked to the superconducting phase itself.The resonance previously has been suggested as contributing a major part of the superconducting condensation (9), measuring directly the condensation fraction (10), and possessing enough magnetic exchange energy to provide the driving force for high-T c superconductivity (11-13), but its small spectral weight compared with spin waves in the AF insulating phase may disqualify the mode from these proposed roles (14). One way to determine the microscopic origin of the resonance is to test its relationship to the superconducting condensation energy.Strictly speaking, the notion of superconducting condensation energy is an ill-defined concept if the normal state fluctuation effects are important as in the case of hole-doped high-T c copper oxides (15,16). However, in t...

Quantum spin excitations through the metal-to-insulator crossover inYBa2Cu3O6+y

“…For underdoped superconducting LSCO (0.055 ≤ x ≤ 0.125), spin excitations have clear incommensurability down to the lowest doping of 0.055 and behave similarly as those for La 1.875 Ba 0.125 CuO 4 19 . Since the resonance appears to be ubiquitous amongst different classes of nearly optimally doped superconducting copper oxides 20,21,22,23 , it is important to determine its doping evolution as the mode may be essential to the mechanism of high-T c superconductivity 24,25,26 . The availability of high quality single crystals of YBCO makes this an ideal system for this study.…”

Magnetic field effect on static antiferromagnetic order and spin excitations in the underdoped iron arsenide superconductor BaFe1.92Ni0.08AsWang1, Luo2, Wang3 et al. 2011Phys. Rev. BSelf Cite369330View full textAdd to dashboardCite

“…One way to test the interplay between magnetism and superconductivity is to use magnetic field as a tuning parameter. If the static AF order in the underdoped BaFe 2−x (Co,Ni) x As 2 indeed coexists and competes with superconductivity [15][16][17][18] , application of a magnetic field that suppresses superconductivity should also enhance the static AF order, much like that of the electron-doped copper oxide superconductors 27,28 . On the other hand, if the static AF order in BaFe 2−x (Co,Ni) x As 2 is chemically phase separated from the superconducting parts of the sample, application of a magnetic field should reduce the AF ordered moment, as has been found in chemically phase separated Ba 1−x K x Fe 2 As 2 29 .…”

Study on Unconventional Superconductivity after the BCS Paradigm

“…This figure is made by quoting to the published data in Ref. [37] gaps on the electron and hole pockets should be opposite. This kind of s-wave gap has been supported by the scanning tunneling experiment already [32], however, the direct evidence is still lacking.…”

“…In Fig.7, we present a combinatory investigation in the Pr 0.88 LaCe 0.12 CuO 4−δ single crystals of the superconducting condensation energy measured through the specific heat and the intensity of the resonance peak, one can see that they both decay with the magnetic field in the same way. [37] Recently in some iron based superconductors, the scanning tunneling spectroscopy measurements also reveal a peak outside the superconducting coherence peak, which is explained as the coupling of the quasiparticles with the resonance mode, a simple ratio Ω ≈ 4.3 ± 0.5k B T c was discovered. [38] This strongly suggests that the neutron resonance is indeed closely related to the superconductivity.…”

“…The Fig.7 here is made based on the published partial data in reference [37], for that we thank Pengcheng Dai and his group members and the authors of that paper. This work was supported by NSF of China, the Ministry of Science and Technology of China (973 projects: 2011CBA00102, 2012CB821403, 2010CB923002) and PAPD.…”