Single crystal growth of YbRh2Si2 and YbIr2Si2

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Abstract

We report on the single crystal growth of the heavy-fermion compounds YbRh2Si2 and YbIr2Si2 using a high-temperature indium-flux technique. The optimization of the initial composition and the temperature-time profile lead to large (up to 100 mg) and clean (\rho_0=0.5 \mu\Omega cm) single crystals of YbRh2Si2. Low-temperature resistivity measurements revealed a sample dependent temperature exponent below 10 K, which for the samples with highest quality deviates from a linear-in-T behaviour. Furthermore, we grew single crystals of the alloy series Yb(Rh_(1-x)Ir_x)2Si2 with 0<x<0.23 and report the structural details. For pure YbIr2Si2, we establish the formation of two crystallographic modifications, where the magnetic 4f-electrons have different physical ground states.

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The break up of heavy electrons at a quantum critical point

F Steglich, P. Coleman, J. Custers … (2003)

The point at absolute zero where matter becomes unstable to new forms of order is called a quantum critical point (QCP). The quantum fluctuations between order and disorder that develop at this point induce profound transformations in the finite temperature electronic properties of the material. Magnetic fields are ideal for tuning a material as close as possible to a QCP, where the most intense effects of criticality can be studied. A previous study on theheavy-electron material \(YbRh_2Si_2\) found that near a field-induced quantum critical point electrons move ever more slowly and scatter off one-another with ever increasing probability, as indicated by a divergence to infinity of the electron effective mass and cross-section. These studies could not shed light on whether these properties were an artifact of the applied field, or a more general feature of field-free QCPs. Here we report that when Germanium-doped \(YbRh_2Si_2\) is tuned away from a chemically induced quantum critical point by magnetic fields there is a universal behavior in the temperature dependence of the specific heat and resistivity: the characteristic kinetic energy of electrons is directly proportional to the strength of the applied field. We infer that all ballistic motion of electrons vanishes at a QCP, forming a new class of conductor in which individual electrons decay into collective current carrying motions of the electron fluid.

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Hall-effect evolution across a heavy-fermion quantum critical point

Qimiao Si, O. Trovarelli, P Gegenwart … (2004)

A quantum critical point (QCP) develops in a material at absolute zero when a new form of order smoothly emerges in its ground state. QCPs are of great current interest because of their singular ability to influence the finite temperature properties of materials. Recently, heavy-fermion metals have played a key role in the study of antiferromagnetic QCPs. To accommodate the heavy electrons, the Fermi surface of the heavy-fermion paramagnet is larger than that of an antiferromagnet. An important unsolved question concerns whether the Fermi surface transformation at the QCP develops gradually, as expected if the magnetism is of spin density wave (SDW) type, or suddenly as expected if the heavy electrons are abruptly localized by magnetism. Here we report measurements of the low-temperature Hall coefficient (\(R_H\)) - a measure of the Fermi surface volume - in the heavy-fermion metal YbRh2Si2 upon field-tuning it from an antiferromagnetic to a paramagnetic state. \(R_H\) undergoes an increasingly rapid change near the QCP as the temperature is lowered, extrapolating to a sudden jump in the zero temperature limit. We interpret these results in terms of a collapse of the large Fermi surface and of the heavy-fermion state itself precisely at the QCP.

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Emerging local Kondo screening and spatial coherence in the heavy-fermion metal YbRh2Si2

Brady Ernst, S. Kirchner, C. Krellner … (2011)

The entanglement of quantum states is both a central concept in fundamental physics and a potential tool for realizing advanced materials and applications. The quantum superpositions underlying entanglement are at the heart of the intricate interplay of localized spin states and itinerant electronic states that gives rise to the Kondo effect in certain dilute magnetic alloys. In systems where the density of localized spin states is sufficiently high, they can no longer be treated as non-interacting; if they form a dense periodic array, a Kondo lattice may be established. Such a Kondo lattice gives rise to the emergence of charge carriers with enhanced effective masses, but the precise nature of the coherent Kondo state responsible for the generation of these heavy fermions remains highly debated. Here we use atomic-resolution tunnelling spectroscopy to investigate the low-energy excitations of a generic Kondo lattice system, YbRh(2)Si(2). We find that the hybridization of the conduction electrons with the localized 4f electrons results in a decrease in the tunnelling conductance at the Fermi energy. In addition, we observe unambiguously the crystal-field excitations of the Yb(3+) ions. A strongly temperature-dependent peak in the tunnelling conductance is attributed to the Fano resonance resulting from tunnelling into the coherent heavy-fermion states that emerge at low temperature. Taken together, these features reveal how quantum coherence develops in heavy 4f-electron Kondo lattices. Our results demonstrate the efficiency of real-space electronic structure imaging for the investigation of strong electronic correlations, specifically with respect to coherence phenomena, phase coexistence and quantum criticality.

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Publication date Created: 22 December 2011

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DOI: 10.1080/14786435.2012.669066

ArXiV ID: 1112.5251

SO-VID: cca66550-5ee1-4bf7-9723-5ada5ae78c0b

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Journal reference Philosophical Magazine, 92:19-21, 2508-2523 (2012)

Comments Invited paper for the Symposium on `Design, Discovery and Growth of Novel Materials' in the Philosophical Magazine

Single crystal growth of YbRh2Si2 and YbIr2Si2

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Most cited references 19

The break up of heavy electrons at a quantum critical point

Hall-effect evolution across a heavy-fermion quantum critical point

Emerging local Kondo screening and spatial coherence in the heavy-fermion metal YbRh2Si2

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