Fundamental conservation laws predict ballistic, i.e., dissipationless transport behaviour in onedimensional quantum magnets. Experimental evidence, however, for such anomalous transport has been lacking ever since. Here we provide experimental evidence for ballistic heat transport in a S = 1/2 Heisenberg chain. In particular, we investigate high purity samples of the chain cuprate SrCuO2 and observe a huge magnetic heat conductivity κmag. An extremely large spinon mean free path of more than a micrometer demonstrates that κmag is only limited by extrinsic scattering processes which is a clear signature of ballistic transport in the underlying spin model. PACS numbers: 75.40.Gb, 75.10.Pq The integrability of the one-dimensional (1D) antiferromagnetic S = 1/2 Heisenberg chain implies highly anomalous transport properties, in particular, a divergent magnetic heat conductivity κ mag at all finite temperatures T . 1-5 This truly ballistic heat transport suggests anomalously large life times and mean free paths of the quantum spin excitations and renders 1D quantum magnets intriguing candidates for spin transport and quantum information processing. 6-8 However, despite the rigorous prediction, experimental evidence for ballistic heat transport in quantum magnets is lacking. Nevertheless, promising large κ mag has been observed in a number of cuprate compounds which realize 1D S = 1/2 Heisenberg antiferromagnets 9-18 with the spin chain material SrCuO 2 being a prominent example 10,18 although a quantitative analysis of κ mag has always been difficult there since the phononic and magnetic heat conductivities are of similar magnitude at low temperature. Such experimental κ mag is always finite since extrinsic scattering processes due to defects and phonons are inherent to all materials and mask the intrinsic behavior of the chain. Formally it seems reasonable to account for the extrinsic scattering via a finite κ mag ∼ D th τ , where τ is a relaxation time, and D th represents the thermal Drude weight which (multiplied by a delta function at zero frequency) describes the intrinsic heat conductivity. In fact, it was thereby possible to identify the expected low-T linearity of D th (T ) in the case of a "dirty" spin chain material where a high density of chain defects generate a large T -independent scattering rate 1/τ . 9In this paper we examine the heat conductivity of SrCuO 2 which is considered an excellent realization of the S = 1/2 Heisenberg chain. [19][20][21] Our samples of extraordinary purity allow an unambiguous separation of the phononic and magnetic contributions to the thermal conductivity. This yields the by far highest κ mag observed 10,13 until now. Our analysis reveals a remarkable lower bound for the low-T limit of the mean free path l mag of more than a micrometer. Thus our data provide striking evidence that the intrinsic heat transport of the S=1/2 Heisenberg chain is indeed ballistic. With increasing temperatures κ mag is increasingly supressed due to spinon-phonon scattering which is the domina...

We have performed inelastic neutron scattering on the near ideal spin-ladder compound La4Sr10Cu24O41 as a starting point for investigating doped ladders and their tendency toward superconductivity. A key feature was the separation of one-triplon and two-triplon scattering. Two-triplon scattering is observed quantitatively for the first time and so access is realized to the important strong magnetic quantum fluctuations. The spin gap is found to be 26.4+/-0.3 meV. The data are successfully modeled using the continuous unitary transformation method, and the exchange constants are determined by fitting to be Jleg=186 meV and Jrung=124 meV along the leg and rung, respectively; a substantial cyclic exchange of Jcyc=31 meV is confirmed.

The magnon thermal conductivity κmag of the spin ladders in Sr14Cu24−xZnxO41 has been investigated at low doping levels x = 0, 0.125, 0.25, 0.5 and 0.75. The Zn-impurities generate nonmagnetic defects which define an upper limit for lmag and therefore allow a clear-cut relation between lmag and κmag to be established independently of any model. Over a large temperature range we observe a progressive suppression of κmag with increasing Zn-content and find in particular that with respect to pure Sr14Cu24O41 κmag is strongly suppressed even in the case of tiny impurity densities where lmag 374 Å. This shows unambiguously that large lmag ≈ 3000 Å which have been reported for Sr14Cu24O41 and La5Ca9Cu24O41 on basis of a kinetic model are in the correct order of magnitude.

We study the impact of a weak bond disorder on the spinon heat transport in the S = 1/2 antiferromagnetic (AFM) Heisenberg chain material Sr1−xCaxCuO2. We observe a drastic suppression in the magnetic heat conductivity κmag even at tiny disorder levels (i.e., Ca-doping levels), in stark contrast to previous findings for κmag of S = 1/2 two-dimensional square lattice and two-leg spinladder systems, where a similar bond disorder has no effect on κmag. Hence, our results underpin the exceptional role of integrability of the S = 1/2 AFM Heisenberg chain model and suggest that the bond disorder effectively destroys the ballistic nature of its heat transport. We further show that the suppression of κmag is captured by an effective spinon-impurity scattering length, which exhibits the same doping dependence as the long-distance exponential decay length of the spin-spin correlation as determined by density-matrix renormalization group calculations.

We report a comparative study of (63)Cu nuclear magnetic resonance spin lattice relaxation rates T(1)(-1) on undoped SrCuO(2) and Ca-doped Sr(0.9)Ca(0.1)CuO(2) spin chain compounds. A temperature independent T(1)(-1) is observed for SrCuO(2) as expected for an S=1/2 Heisenberg chain. Surprisingly, we observe an exponential decrease of T(1)(-1) for T<90 K in the Ca-doped sample evidencing the opening of a spin gap. The data analysis within the J(1)-J(2) Heisenberg model employing density-matrix renormalization group calculations suggests an impurity driven small alternation of the J(2)-exchange coupling as a possible cause of the spin gap.

Abstract:We have investigated the low-energy electronic structure of the strongly correlated one-dimensional copper oxide chain compound SrCuO 2 by angle resolved photoemission as a function of excitation energy. In addition to the prominent spinon-holon continuum we observe a peaklike and dispersive feature at the zone boundary. By finetuning the experimental parameters we are able to monitor the full holon branch and to directly measure the electronic hopping parameter with unprecedented accuracy.1 One-dimensional cuprates attract the attention of solid-state physicists for many reasons.Among them almost perfect examples of one dimensional spin ½ Heisenberg chains can be found [1,2]. It is well known that the standard models for the description of their lowenergy electronic excitations spectacularly fail: a single electronic excitation decomposes into two independent excitations carrying either spin (spinons) or charge (holons) [3,4].While being conceptually highly important in its own right, the spin-charge separation promotes another striking peculiarity of these systems, namely the large non-linear optical response, which renders these materials even technologically interesting [5,6]. More specifically, external electrical fields tune the optical parameters enabling the construction of optical switches [7]. Furthermore, the close structural and electronic relationship of these materials to the high-temperature superconductors (HTSC), and the known instabilities of the HTSC towards one-dimensional phenomena, forms a background, which provides a strong motivation for close scrutiny [8].The first direct observation of the spin-charge separation was achieved by angle-resolved photoemission (ARPES) in SrCuO 2 [9]. It was found that the bandwidth of the lowest electronic excitation in SrCuO 2 scales with t , the electronic hopping parameter, rather than J, the exchange constant, in striking contrast to the two dimensional insulator Sr 2 CuO 2 Cl 2 . This is a clear indication that the electronic excitations are decoupled from the spin background in the one dimensional case. Subsequent photoemission studies confirmed and substantiated the picture of the spin-charge separation [10,11]. In particular, the spinon band has been explicitly resolved for the closely related compound Sr 2 CuO 3 [12,13] From the theoretical side the derivation of the spectral function of one-dimensional Mott systems has been the subject of intense effort [19,20]. A crucial precondition for comparison with experiment is the reliable knowledge of the basic electronic parameters like t and J. In this letter we show that previous low-energy photoemission studies tend to underestimate the holon bandwidth -and therefore t -and provide a measurement of t with unprecedented accuracy.Eventually, the validity of the spin-charge separation description has been challenged recently by x-ray ARPES [18]. We explicitly show here that major predictions concerning the spinon and holon dispersion relations are fulfilled, which confirms the legitimacy of an e...

Recent works in mechanical fatigue consider that a threshold of entropy exists, the fracture fatigue entropy. The determination of this quantity is usually done considering empirical models for the mechanical power estimation. In this paper, we experimentally observe the existence of a threshold of entropy and exergy in low cycle fatigue for a flat Al-2024 specimen avoiding the use of a model, solely measuring the heat generated during a fatigue test. Results are then compared considering various hypotheses (1D heat dissipation with convection and radiation considered as heat sources, and, heat transfer from a fin with convection and radiation as boundary conditions) to an empirical mechanical model known in the literature and deviations between them are discussed.

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