We investigate the energy exchanges along an electronic quantum channel realized in the integer quantum Hall regime at filling factor νL = 2. One of the two edge channels is driven out-ofequilibrium and the resulting electronic energy distribution is measured in the outer channel, after several propagation lengths 0.8 µm≤ L ≤ 30 µm. Whereas there are no discernable energy transfers toward thermalized states, we find efficient energy redistribution between the two channels without particle exchanges. At long distances L ≥ 10 µm, the measured energy distribution is a hot Fermi function whose temperature is lower than expected for two interacting channels, which suggests the contribution of extra degrees of freedom. The observed short energy relaxation length challenges the usual description of quantum Hall excitations as quasiparticles localized in one edge channel.PACS numbers: 73.43. Fj, 72.15.Lh, 73.23.Ad, 73.43.Lp The basic manifestation of the quantum Hall effect is a quantized Hall resistance R H = h/e 2 ν L , accompanied by a vanishing longitudinal resistance. In this regime, quantization of the two-dimensional cyclotron motion opens a large gap separating Landau levels in the bulk of the sample from the Fermi energy. The only available low energy excitations propagate along the edges, where the Landau levels cross the Fermi energy. The effective edge state theory suggests these excitations are prototypal one-dimensional chiral fermions (1DCF) [1], each of the ν L edge channels (EC) being identified with a onedimensional conductor. Because back-scattering is forbidden by chirality, ECs are considered to be ideal ballistic quantum channels. Their similitude with light beams has inspired electronic analogues of quantum optics experiments [2-5] and proposals for quantum information applications [6]. However, the nature and decoherence of edge excitations are poorly understood, as highlighted by unexpected results obtained with electronic MachZehnder interferometers: an unusual energy dependence of the interference fringes' visibility [2, 7], a non-gaussian noise [8] and a short coherence length [9, 10]. Interactions between ECs and with their environment are seen as the key ingredient to explain these results (see e.g. [11, 12]).In the present experimental work, we investigate the interaction mechanisms taking place along an EC through the energy exchanges they induce. A similar approach was previously used on mesoscopic metal wires [13] and on carbon nanotubes [14]. Here we focus on the filling factor ν L = 2, where two co-propagating ECs are present, and at which the above unexpected results were observed. Our experiment relies on the techniques we recently demonstrated to drive out-of-equilibrium an EC and to measure the resulting energy distribution f (E) of 1DCF quasiparticles [15]. There, we drove out-ofequilibrium only the outer EC, and f (E) was measured in the same EC after a short 0.8 µm propagation distance, for which the energy redistribution is negligible. Here, we drive out-of-equilibrium sel...

Heat transport has large potentialities to unveil new physics in mesoscopic systems. A striking illustration is the integer quantum Hall regime 1 , where the robustness of Hall currents limits information accessible from charge transport 2 . Consequently, the gapless edge excitations are incompletely understood. The effective edge states theory describes them as prototypal one-dimensional chiral fermions 3,4 -a simple picture that explains a large body of observations 5 and calls for quantum information experiments with quantum point contacts in the role of beam splitters 6,7,8,9,10,11 . However, it is in ostensible disagreement with the prevailing theoretical framework that predicts, in most situations 12 , additional gapless edge modes 13 . Here, we present a setup which gives access to the energy distribution, and consequently to the energy current, in an edge channel brought out-of-equilibrium. This provides a stringent test of whether the additional states capture part of the injected energy. Our results show it is not the case and thereby demonstrate regarding energy transport, the quantum optics analogy of quantum point contacts and beam splitters. Beyond the quantum Hall regime, this novel spectroscopy technique opens a new window for heat transport and out-of-equilibrium experiments.The integer quantum Hall effect, discovered nearly thirty years ago 1 , has recently experienced a strong revival driven by milestone experiments toward quantum information with edge states 8,9,14 .Beyond Hall currents, new phenomena have emerged that were unexpected within the free one-dimensional chiral fermions (1DCF) model.The on-going debate triggered by electronic Mach-Zehnder interferometers experiments 8,15,16,17 vividly illustrates the gaps in our understanding. Coulomb interaction is seen as the key ingredient. In addition to its most striking repercussion, the fractional quantum Hall effect 18 , the edge reconstruction (ER) turns out to have deep implications on edge excitations. This phenomenon results from the competition between Coulomb interaction that tends to spread the electronic fluid, and the confinement potential: as the latter gets smoother, the non-interacting edge becomes unstable 19 . Theory predicts new branches of gapless electronic excitations in reconstructed edges 13,20 , which breaks the mapping of an edge channel (EC) onto 1DCF and, possibly, the promising quantum optics analogy. For most edges realized in semi-conductor heterojunctions (except by cleaved edge overgrowth 21 ), ER results in wide compressible ECs separated by narrow incompressible strips 12 and the new excited states are overall neutral internal charge oscillations across the ECs width 13 .In practice, the predicted additional neutral modes areExperimental implementation of nonequilibrium edge channel spectroscopy. a, Schematic description of the energy distributions fD,S(E) spectroscopy with a single active electronic level of tunable energy E lev (VG) in the quantum dot (QD). b, The current IQD (∂IQD/∂VG) is proportional to...

This paper reports on the development of a technology involving 100 Mo-enriched scintillating bolometers, compatible with the goals of CUPID, a proposed nextgeneration bolometric experiment to search for neutrinoless double-beta decay. Large mass (∼ 1 kg), high optical quality, radiopure 100 Mo-containing zinc and lithium molybdate crystals have been produced and used to develop high performance single detector modules based on 0.2-0.4 kg scintillating bolometers. In particular, the energy resolution of the lithium molybdate detectors near the Q-value of the doublebeta transition of 100 Mo (3034 keV) is 4-6 keV FWHM. The rejection of the α-induced dominant background above 2.6 MeV is better than 8σ . Less than 10 µBq/kg activity of 232 Th ( 228 Th) and 226 Ra in the crystals is ensured by boule recrystallization. The potential of 100 Mo-enriched scintillating bolometers to perform high sensitivity double-beta decay searches has been demonstrated with only 10 kg×d exposure: the two neutrino double-beta decay half-life of 100 Mo has been measured with the up-to-date highest accuracy as T 1/2 = [6.90 ± 0.15(stat.) ± 0.37(syst.)] × 10 18 years. Both crystallization and detector technologies favor lithium molybdate, which has been selected for the ongoing construction of the CUPID-0/Mo demonstrator, containing several kg of 100 Mo.