Localized Magnetic Impurity States In Metals: Some Experimental Relationships

Daybell, M. D.; Steyert, W.A.

doi:10.1103/revmodphys.40.380

Cited by 293 publications

(156 citation statements)

References 104 publications

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“…If such a spatially extended state occurs, one would then expect to see its experimental signature on local magnetic measurements in the corresponding spatial range around the impurity, so that NMR experiments would be the ideal probe to view such effects. From the study of the macroscopic properties of impurities in noble metal hosts, it was established that the crossover temperature T K was highly dependent on the impurity [22]. This was of course quite compatible with the exponential expression of Eq.…”

Section: The Kondo Problemsupporting

confidence: 59%

From Friedel Oscillations and Kondo Effect to the Pseudogap in Cuprates

Alloul

2012

J Supercond Nov Magn

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Abstract. One of the great achievements performed by Jacques Friedel in France has been to promote experimental activities on the electronic properties in condensed matter physics, which has led him, among others, to be an active promoter of the up-rise of the "Laboratoire de Physique des Solides" (LPS). I have had the chance to be involved in this process in the early days and to create a Nuclear Magnetic Resonance (NMR) group which remains active nowadays. Among various other scientific activities, I have performed some work on Kondo effect in the 1970's which has allowed me to enlighten the real interest of the NMR probe as a local experimental technique to visualize the perturbation brought by impurities in normal metals. These experiments were of course driven by my strong exposure to J. Friedel's education on charge and spin density oscillations in metals. This work has been also my first personal contact with correlated electron physics, a field in which I have been involved for years particularly since the discovery of high T c cuprates (HTSC). I recall that the early NMR experiments done in these systems have given evidence for the existence of strong electronic correlations and established the occurrence of the "pseudogap", on which I have initially had some exchanges with J. Friedel. The pseudogap, occurring below a temperature T*, has during the last twenty years raised endless discussions about the incidence of correlations on superconductivity. Many researchers are still advocating today that the pseudogap is due to the existence of preformed pairs above T c . I shall show that its robustness to impurities and disorder that we evidenced from the early days rather suggested that it results from a competing order of the correlated state. This is apparently better accepted nowadays, although various distinct ordered states detected below T* are not yet understood. The short reviews of the work done on Kondo effect and on the cuprates in Orsay allow me to enlighten the importance of the initial choices done by J. Friedel for the LPS. I also underline the large contrast between the scientific behaviours which prevailed between these two periods of scientific activity. This is not only ascribed to the discovery of the HTSC but also to the changes in publication policies and to the modification of evaluation procedures, all this being driven by the advent of information technologies. I suggest that these changes might have a negative incidence, in my opinion, on the research and education system, at least in our field of science.

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Section: The Kondo Problemsupporting

confidence: 59%

From Friedel Oscillations and Kondo Effect to the Pseudogap in Cuprates

Alloul

2012

J Supercond Nov Magn

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“…Many phenomena in strongly correlated electron physics, especially for heavy-fermion metals such as unconventional superconductivity or quantum critical behaviour are attributed to the competition of RKKY interaction with Kondo physics 5 . While single-impurity Kondo physics, where the impurities can be treated individually, has been studied for a long time in macroscopic measurements 6 and more recently in nanostructures [7][8][9][10][11][12][13][14][15][16][17][18] a detailed knowledge of the transition towards a systems of interacting impurities is still lacking.…”

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confidence: 99%

Interplay between the Kondo effect and the Ruderman–Kittel–Kasuya–Yosida interaction

et al. 2014

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The interplay between the Ruderman-Kittel-Kasuya-Yosida interaction and the Kondo effect is expected to provide the driving force for the emergence of many phenomena in strongly correlated electron materials. Two magnetic impurities in a metal are the smallest possible system containing all these ingredients and define a bottom-up approach towards a longterm understanding of concentrated/dense systems. Here we report on the experimental and theoretical investigation of iron dimers buried below a Cu(100) surface by means of lowtemperature scanning tunnelling spectroscopy combined with density functional theory and numerical renormalization group calculations. The Kondo effect, in particular the width of the Abrikosov-Suhl resonance, is strongly altered or even suppressed due to magnetic coupling between the impurities. It oscillates as a function of dimer separation revealing that it is related to indirect exchange interactions mediated by the conduction electrons.

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“…A 10% contribution of the background, corresponding to a = 0.1, reduces the figure of merit to 25% of its original value for a = 0. However, in mixed-valence alloys, the f-level contribution to the density of states is typically larger than 100 times the background value (10,11). In this case, the negative effect on ZT of the background contribution is small.…”

Section: Zt=1 _k0mentioning

confidence: 98%

The best thermoelectric.

Mahan

Sofo

1996

Proc. Natl. Acad. Sci. U.S.A.

1,501

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What electronic structure provides the largest figure of merit for thermoelectric materials? To answer that question, we write the electrical conductivity, thermopower, and thermal conductivity as integrals of a single function, the transport distribution. Then we derive the mathematical function for the transport distribution, which gives the largest figure of merit. A delta-shaped transport distribution is found to maximize the thermoelectric properties. This result indicates that a narrow distribution of the energy of the electrons participating in the transport process is needed for maximum thermoelectric efficiency. Some possible realizations of this idea are discussed.Thermoelectric materials can be used to make refrigerators or power generators (1, 2). These solid state devices have no moving parts and are extremely reliable. Their efficiency is low, so they are used in products where reliability is more important than efficiency. Thermoelectric refrigerators are used to spot cool electronic components such as infrared sensors or computer chips. Power generators are used in space stations and satellites.There has been much effort to find the best thermoelectric materials (1-3). There has also been numerous discussion of the physical limits-i.e., what are the best possible thermoelectrics allowed by nature (4)? Here we provide a new and simple estimate of the maximum efficiency of thermoelectric materials. The efficiency of thermoelectric energy converters depends on the transport coefficients of the constituent materials through the figure of merit (1): a-S2where a-is the electrical conductivity and S is the Seebeck coefficient. The quantity in the denominator is the thermal conductivity; it is given by the sum of contributions from the electronic carriers Ke and the lattice KI. The efficiency is increased by making ZT as large as possible, where T is the mean operating temperature of the device. At room temperature, the best thermoelectric material now known is Bi2Te3, which has ZT 1 (1, 2). With this value, the coefficient of performance of thermoelectric coolers is about one-third the value for conventional compressor systems. At room temperature, with the current design, thermoelectric refrigerators will be competitive with conventional compressor systems if a material is found with ZT 4. However, any small increment in this value (ZT 2 1) will result in many new applications for these devices. This technology is environmentally cleaner and more reliable than traditional compressor systems. Therefore, it is worth exploring the possibility of increasing ZT to find a material with ZT >

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Localized Magnetic Impurity States In Metals: Some Experimental Relationships

Cited by 293 publications

References 104 publications

From Friedel Oscillations and Kondo Effect to the Pseudogap in Cuprates

From Friedel Oscillations and Kondo Effect to the Pseudogap in Cuprates

Interplay between the Kondo effect and the Ruderman–Kittel–Kasuya–Yosida interaction

The best thermoelectric.

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