The phase diagrams of the high temperature superconductors

Transcription

1 The phase diagrams of the high temperature superconductors Talk online: sachdev.physics.harvard.edu HARVARD

2 Max Metlitski, Harvard Eun Gook Moon, Harvard HARVARD

3 The cuprate superconductors

4 Square lattice antiferromagnet H = ij J ij Si S j Ground state has long-range Néel order Order parameter is a single vector field ϕ = η isi η i = ±1 on two sublattices ϕ = 0 in Néel state.

5 The cuprate superconductors Antiferromagnet d-wave superconductor

6 The cuprate superconductors Incommensurate/ disordered antiferromagnetism and charge order Antiferromagnet d-wave superconductor

7 The cuprate superconductors Incommensurate/ disordered antiferromagnetism and charge order Antiferromagnet Pseudogap d-wave superconductor

8 The cuprate superconductors Incommensurate/ disordered antiferromagnetism and charge order Antiferromagnet Pseudogap d-wave superconductor

9 The cuprate superconductors Incommensurate/ disordered antiferromagnetism and charge order Antiferromagnet Strange Metal Pseudogap d-wave superconductor

10 Strange Metal Γ Γ

11 Key Ingredients: Strange Metal Γ Γ

12 Key Ingredients: Antiferromagnetism (AF) Spin density wave (SDW) Strange Metal Γ Γ

13 Key Ingredients: d-wave superconductivity Antiferromagnetism (AF) Spin density wave (SDW) Strange Metal Γ Γ

14 Key Ingredients: d-wave superconductivity Antiferromagnetism (AF) Spin density wave (SDW) Fermi surface change Strange Metal Γ Γ

15 Holedoped Electrondoped

16 Electron-doped cuprate superconductors Holedoped Electrondoped

17 Electron-doped cuprate superconductors n 2 Holedoped Electrondoped Figure prepared by K. Jin and and R. L. Greene based on N. P. Fournier, P. Armitage, and R. L. Greene, Rev. Mod. Phys. 82, 2421 (2010). Resistivity ρ 0 + AT n

18 Electron-doped cuprate superconductors n 2 Holedoped Electrondoped Figure prepared by K. Jin and and R. L. Greene based on N. P. Fournier, P. Armitage, and R. L. Greene, Rev. Mod. Phys. 82, 2421 (2010). Resistivity ρ 0 + AT n

19 Electron-doped cuprate superconductors Strange Metal n Holedoped Electrondoped 1 Figure prepared by K. Jin and and R. L. Greene based on N. P. Fournier, P. Armitage, and R. L. Greene, Rev. Mod. Phys. 82, 2421 (2010). Resistivity ρ 0 + AT n

20 Iron pnictides: a new class of high temperature superconductors

21 Iron pnictides: a new class of high temperature superconductors Ort Tet Ishida, Nakai, and Hosono arxiv: v1 50 AFM / Ort 0 SC S. Nandi, M. G. Kim, A. Kreyssig, R. M. Fernandes, D. K. Pratt, A. Thaler, N. Ni, S. L. Bud'ko, P. C. Canfield, J. Schmalian, R. J. McQueeney, A. I. Goldman, Physical Review Letters 104, (2010).

22 Temperature-doping phase diagram of the iron pnictides: BaFe 2 (As 1-x P x ) 2 T 0 T SDW T c SDW! " Resistivity ρ 0 + AT α Superconductivity 0 S. Kasahara, T. Shibauchi, K. Hashimoto, K. Ikada, S. Tonegawa, R. Okazaki, H. Shishido, H. Ikeda, H. Takeya, K. Hirata, T. Terashima, and Y. Matsuda, Physical Review B 81, (2010)

23 Temperature-doping phase diagram of the iron pnictides: BaFe 2 (As 1-x P x ) 2 T 0 T SDW T c SDW! " Resistivity ρ 0 + AT α Superconductivity 0 S. Kasahara, T. Shibauchi, K. Hashimoto, K. Ikada, S. Tonegawa, R. Okazaki, H. Shishido, H. Ikeda, H. Takeya, K. Hirata, T. Terashima, and Y. Matsuda, Physical Review B 81, (2010)

24 Temperature-doping phase diagram of the iron pnictides: Strange Metal BaFe 2 (As 1-x P x ) 2 T 0 T SDW T c! " SDW Resistivity ρ 0 + AT α Superconductivity 0 S. Kasahara, T. Shibauchi, K. Hashimoto, K. Ikada, S. Tonegawa, R. Okazaki, H. Shishido, H. Ikeda, H. Takeya, K. Hirata, T. Terashima, and Y. Matsuda, Physical Review B 81, (2010)

25 Lower Tc superconductivity in the heavy fermion compounds a CePd2Si2 N. D. Mathur, F. M. Grosche, S. R. Julian, I. R. Walker, D. M. Freye, R. K. W. Haselwimmer, and G. G. Lonzarich, Nature 394, 39 (1998)

26 Lower Tc superconductivity in the heavy fermion compounds G. Knebel, D. Aoki, and J. Flouquet, arxiv:

27 Questions Can quantum fluctuations near the loss of antiferromagnetism induce higher temperature superconductivity?

28 Questions Can quantum fluctuations near the loss of antiferromagnetism induce higher temperature superconductivity? If so, why is there no antiferromagnetism in the hole-doped cuprates near the point where the superconductivity is strongest?

29 Questions Can quantum fluctuations near the loss of antiferromagnetism induce higher temperature superconductivity? If so, why is there no antiferromagnetism in the hole-doped cuprates near the point where the superconductivity is strongest? What is the physics of the strange metal?

30 Outline 1. Loss of antiferromagnetism in an insulator Coupled-dimer antiferromagnets and quantum criticality 2. Onset of antiferromagnetism in a metal From large Fermi surfaces to Fermi pockets, d-wave superconductivity, and competing orders 3. Strongly-coupled quantum criticality in metals The AdS/CFT correspondence

31 Outline 1. Loss of antiferromagnetism in an insulator Coupled-dimer antiferromagnets and quantum criticality 2. Onset of antiferromagnetism in a metal From large Fermi surfaces to Fermi pockets, d-wave superconductivity, and competing orders 3. Strongly-coupled quantum criticality in metals The AdS/CFT correspondence

32 Square lattice antiferromagnet H = ij J ij Si S j Ground state has long-range Néel order Order parameter is a single vector field ϕ = η isi η i = ±1 on two sublattices ϕ = 0 in Néel state.

33 Square lattice antiferromagnet H = ij J ij Si S j J J/λ Weaken some bonds to induce spin entanglement in a new quantum phase

34 Square lattice antiferromagnet H = ij J ij Si S j J J/λ Ground state is a quantum paramagnet with spins locked in valence bond singlets = 1 2

35 = 1 2 λ c λ

36 = 1 2 λ c λ Pressure in TlCuCl3 A. Oosawa, K. Kakurai, T. Osakabe, M. Nakamura, M. Takeda, and H. Tanaka, Journal of the Physical Society of Japan, 73, 1446 (2004).

37 TlCuCl 3 An insulator whose spin susceptibility vanishes exponentially as the temperature T tends to zero.

38 TlCuCl 3 Quantum paramagnet at ambient pressure

39 TlCuCl 3 Neel order under pressure A. Oosawa, K. Kakurai, T. Osakabe, M. Nakamura, M. Takeda, and H. Tanaka, Journal of the Physical Society of Japan, 73, 1446 (2004).

40 = 1 2 λ c λ

41 Excitation spectrum in the paramagnetic phase λ c Spin S =1 λ triplon

42 Excitation spectrum in the paramagnetic phase λ c Spin S =1 λ triplon

43 Excitation spectrum in the paramagnetic phase λ c Spin S =1 λ triplon

44 Excitation spectrum in the paramagnetic phase λ c Spin S =1 λ triplon

45 Excitation spectrum in the paramagnetic phase λ c Spin S =1 triplon λ

46 Excitation spectrum in the Néel phase λ c λ Spin waves

47 Excitation spectrum in the Néel phase λ c λ Spin waves

48 Excitation spectrum in the Néel phase λ c λ Spin waves

49 TlCuCl 3 with varying pressure Energy [mev] Pressure [kbar] Observation of 3 2 low energy modes, emergence of new Higgs particle in the Néel phase. Christian Ruegg, Bruce Normand, Masashige Matsumoto, Albert Furrer, Desmond McMorrow, Karl Kramer, Hans Ulrich Gudel, Severian Gvasaliya, Hannu Mutka, and Martin Boehm, Phys. Rev. Lett. 100, (2008)

50 = 1 2 λ c λ Quantum critical point with non-local entanglement in spin wavefunction

51 Description using Landau-Ginzburg field theory λ c CFT3 O(3) order parameter ϕ ( S = d 2 rdτ τ ϕ ) 2 + c 2 ( r ϕ ) 2 +(λ λ c )ϕ 2 + u ϕ 2 2 λ

52 S. Sachdev and J. Ye, Phys. Rev. Lett. 69, 2411 (1992). A. V. Chubukov, S. Sachdev, and J. Ye, Phys. Rev. B 49, (1994). Quantum critical Classical spin waves Dilute triplon gas Neel order Pressure in TlCuCl3

53 S. Sachdev and J. Ye, Phys. Rev. Lett. 69, 2411 (1992). A. V. Chubukov, S. Sachdev, and J. Ye, Phys. Rev. B 49, (1994). CFT3 at T>0 Quantum critical Classical spin waves Dilute triplon gas Neel order Pressure in TlCuCl3

54 S. Sachdev and J. Ye, Phys. Rev. Lett. 69, 2411 (1992). A. V. Chubukov, S. Sachdev, and J. Ye, Phys. Rev. B 49, (1994). CFT3 at T>0 Quantum critical Classical spin waves Dilute triplon gas Neel order Pressure in TlCuCl3

55 S. Sachdev and J. Ye, Phys. Rev. Lett. 69, 2411 (1992). A. V. Chubukov, S. Sachdev, and J. Ye, Phys. Rev. B 49, (1994). CFT3 at T>0 Classical spin waves Quantum critical Strongly coupled dynamics and transport with no Dilute triplon gas particle/wave interpretation, and relaxation thermal equilibration times are universally proportional to /k B T Neel order Pressure in TlCuCl3

56 Outline 1. Loss of antiferromagnetism in an insulator Coupled-dimer antiferromagnets and quantum criticality 2. Onset of antiferromagnetism in a metal From large Fermi surfaces to Fermi pockets, d-wave superconductivity, and competing orders 3. Strongly-coupled quantum criticality in metals The AdS/CFT correspondence

57 Outline 1. Loss of antiferromagnetism in an insulator Coupled-dimer antiferromagnets and quantum criticality 2. Onset of antiferromagnetism in a metal From large Fermi surfaces to Fermi pockets, d-wave superconductivity, and competing orders 3. Strongly-coupled quantum criticality in metals The AdS/CFT correspondence

58 Central ingredients in cuprate phase diagram: antiferromagnetism, superconductivity, and change in Fermi surface Strange Metal Γ Γ

59 Fermi surface+antiferromagnetism Metal with large Fermi surface

60 Fermi surface+antiferromagnetism Metal with large Fermi surface + The electron spin polarization obeys S(r, τ) = ϕ (r, τ)e ik r where K is the ordering wavevector.

61 Fermi surface+antiferromagnetism ncreasing SDW ϕ =0 ϕ =0 Metal with electron and hole pockets Metal with large Fermi surface s S. Sachdev, A. V. Chubukov, and A. Sokol, Phys. Rev. B 51, (1995). A. V. Chubukov and D. K. Morr, Physics Reports 288, 355 (1997).

62 Evidence for small Fermi pockets Suchitra E. Sebastian, N. Harrison, M. M. Altarawneh, Ruixing Liang, D. A. Bonn, W. N. Hardy, and G. G. Lonzarich Physical Review B 81, (R) (2010) Original observation: N. Doiron-Leyraud, C. Proust, D. LeBoeuf, J. Levallois, J.-B. Bonnemaison, R. Liang, D. A. Bonn, W. N. Hardy, and L. Taillefer, Nature 447, 565 (2007)

63 Fermi surface+antiferromagnetism ncreasing SDW ϕ =0 ϕ =0 Metal with electron and hole pockets Metal with large Fermi surface s S. Sachdev, A. V. Chubukov, and A. Sokol, Phys. Rev. B 51, (1995). A. V. Chubukov and D. K. Morr, Physics Reports 288, 355 (1997).

64 Theory of quantum criticality in the cuprates T * Fluctuating Fermi pockets Quantum Strange Critical Metal Large Fermi surface ncreasing SDW Spin density wave (SDW) Underlying SDW ordering quantum critical point in metal at x = x m

65 Theory of quantum criticality in the cuprates T * Fluctuating Fermi pockets Quantum Strange Critical Metal Large Fermi surface ncreasing SDW Spin density wave (SDW) Relaxation and equilibration times /k B T are robust properties of strongly-coupled quantum criticality

66 Theory of quantum criticality in the cuprates T * Fluctuating Fermi pockets Quantum Strange Metal Critical? Large Fermi surface ncreasing SDW Spin density wave (SDW) Relaxation and equilibration times /k B T are robust properties of strongly-coupled quantum criticality

67 Physical Review B 34, 8190 (1986)

68 Theory of quantum criticality in the cuprates T * Fluctuating Fermi pockets Quantum Strange Metal Critical? Large Fermi surface ncreasing SDW Spin density wave (SDW) Relaxation and equilibration times /k B T are robust properties of strongly-coupled quantum criticality

69 Theory of quantum criticality in the cuprates Fluctuating, Small Fermi paired pockets Fermi with pairing pockets fluctuations Strange Metal d-wave superconductor Large Fermi surface M. A. Metlitski and S. Sachdev, Physical Review B 82, (2010) Spin density wave (SDW) SDW quantum critical point is unstable to d-wave superconductivity This instability is stronger than that in the BCS theory

70 Temperature-doping phase diagram of the iron pnictides: Strange Metal BaFe 2 (As 1-x P x ) 2 T 0 T SDW T c! " SDW Resistivity ρ 0 + AT α Superconductivity 0 S. Kasahara, T. Shibauchi, K. Hashimoto, K. Ikada, S. Tonegawa, R. Okazaki, H. Shishido, H. Ikeda, H. Takeya, K. Hirata, T. Terashima, and Y. Matsuda, Physical Review B 81, (2010)

71 The cuprate superconductors Incommensurate/ disordered antiferromagnetism and charge order Antiferromagnet Strange Metal Pseudogap d-wave superconductor

72 Theory of quantum criticality in the cuprates Fluctuating, Small Fermi paired pockets Fermi with pairing pockets fluctuations Strange Metal d-wave superconductor Large Fermi surface M. A. Metlitski and S. Sachdev, Physical Review B 82, (2010) Spin density wave (SDW) SDW quantum critical point is unstable to d-wave superconductivity This instability is stronger than that in the BCS theory

73 Theory of quantum criticality in the cuprates Fluctuating, Small Fermi paired pockets Fermi with pairing pockets fluctuations Strange Metal d-wave superconductor Large Fermi surface E. G. Moon and S. Sachdev, Phy. Rev. B 80, (2009) Spin density wave (SDW) Competition between SDW order and superconductivity moves the actual quantum critical point to x = x s <x m.

74 Theory of quantum criticality in the cuprates Fluctuating, Small Fermi paired pockets Fermi with pairing pockets fluctuations Strange Metal d-wave superconductor Large Fermi surface E. G. Moon and S. Sachdev, Phy. Rev. B 80, (2009) Spin density wave (SDW) Competition between SDW order and superconductivity moves the actual quantum critical point to x = x s <x m.

75 Theory of quantum criticality in the cuprates Fluctuating, paired paired Fermi Fermi pockets pockets Strange Metal d-wave superconductor Large Fermi surface E. G. Moon and S. Sachdev, Phy. Rev. B 80, (2009) Spin density wave (SDW) Competition between SDW order and superconductivity moves the actual quantum critical point to x = x s <x m.

76 T * Fluctuating, paired Fermi pockets Strange Metal Large Fermi surface d-wave superconductor Spin density wave (SDW)

77 E. Demler, S. Sachdev and Y. Zhang, Phys. Rev. Lett. 87, (2001). T T * Fluctuating, Small Fermi pockets paired Fermi with pairing pockets fluctuations Strange Metal Large Fermi surface T sdw d-wave SC SC+ SDW SC SDW (Small Fermi pockets) H M "Normal" (Large Fermi surface)

78 E. Demler, S. Sachdev and Y. Zhang, Phys. Rev. Lett. 87, (2001). T T * Fluctuating, Small Fermi pockets paired Fermi with pairing pockets fluctuations Strange Metal Large Fermi surface T sdw d-wave SC SC+ SDW SC Quantum oscillations SDW (Small Fermi pockets) M H "Normal" (Large Fermi surface)

79 E. Demler, S. Sachdev and Y. Zhang, Phys. Rev. Lett. 87, (2001). T T * Fluctuating, Small Fermi pockets paired Fermi with pairing pockets fluctuations Strange Metal Large Fermi surface Many experiments have presented evidence for the predicted green quantum phase transition line from SC to SC +SDW in a magnetic field SDW (Small Fermi pockets) H T sdw SC+ SDW d-wave SC M SC "Normal" (Large Fermi surface)

80 Similar phase diagram for CeRhIn5 G. Knebel, D. Aoki, and J. Flouquet, arxiv:

81 Iron pnictides: a new class of high temperature superconductors Ort Tet Ishida, Nakai, and Hosono arxiv: v1 50 AFM / Ort 0 SC S. Nandi, M. G. Kim, A. Kreyssig, R. M. Fernandes, D. K. Pratt, A. Thaler, N. Ni, S. L. Bud'ko, P. C. Canfield, J. Schmalian, R. J. McQueeney, A. I. Goldman, Physical Review Letters 104, (2010).

82 Outline 1. Loss of antiferromagnetism in an insulator Coupled-dimer antiferromagnets and quantum criticality 2. Onset of antiferromagnetism in a metal From large Fermi surfaces to Fermi pockets, d-wave superconductivity, and competing orders 3. Strongly-coupled quantum criticality in metals The AdS/CFT correspondence

83 Outline 1. Loss of antiferromagnetism in an insulator Coupled-dimer antiferromagnets and quantum criticality 2. Onset of antiferromagnetism in a metal From large Fermi surfaces to Fermi pockets, d-wave superconductivity, and competing orders 3. Strongly-coupled quantum criticality in metals The AdS/CFT correspondence

84 Quantum criticality of the onset of antiferromagnetism in a metal ncreasing ϕ =0SDW ϕ =0 Metal with electron and hole pockets Metal with large Fermi surface s

85 Quantum criticality of the onset of antiferromagnetism in a metal ncreasing ϕ =0SDW ϕ =0 Metal with electron and hole pockets Metal with large Fermi surface s

86 Quantum criticality of the onset of antiferromagnetism in a metal ncreasing ϕ =0SDW ϕ =0 Metal with electron and hole pockets Metal with large Fermi surface s

87 Quantum criticality of the onset of antiferromagnetism in a metal ncreasing ϕ =0SDW ϕ =0 Metal with electron and hole pockets Metal with large Fermi surface s Quantum critical theory is strongly-coupled in two (but not higher) spatial dimensions (but not a CFT). M.A. Metlitski and S. Sachdev, Physical Review B 82, (2010)

88 Field theories in D spacetime dimensions are characterized by couplings g which obey the renormalization group equation u dg du = β(g) where u is the energy scale. The RG equation is local in energy scale, i.e. the RHS does not depend upon u.

89 Field theories in D spacetime dimensions are characterized by couplings g which obey the renormalization group equation u dg du = β(g) where u is the energy scale. The RG equation is local in energy scale, i.e. the RHS does not depend upon u. Key idea: Implement u as an extra dimension, and map to a local theory in D+1 dimensions.

90 u J. McGreevy, arxiv

91 At the RG fixed point, β(g) = 0, the D dimensional field theory is invariant under the scale transformation x µ x µ /b, u bu

92 At the RG fixed point, β(g) = 0, the D dimensional field theory is invariant under the scale transformation x µ x µ /b, u bu This is an invariance of the metric of the theory in D + 1 dimensions. The unique solution is ds 2 = u L 2 dx µ dx µ + L 2 du2 u 2. Or, using the length scale z = L 2 /u ds 2 = L 2 dxµ dx µ + dz 2 z 2. This is the space AdS D+1, and L is the AdS radius.

93 J. McGreevy, arxiv

94 AdS/CFT correspondence The quantum theory of a black hole in a 3+1- dimensional negatively curved AdS universe is holographically represented by a CFT (the theory of a 3+1 dimensional AdS space quantum critical point) in 2+1 dimensions Maldacena, Gubser, Klebanov, Polyakov, Witten

95 AdS/CFT correspondence The quantum theory of a black hole in a 3+1- dimensional negatively curved AdS universe is holographically represented by a CFT (the theory of a quantum critical point) in 2+1 dimensions 3+1 dimensional AdS space A 2+1 dimensional system at its quantum critical point Maldacena, Gubser, Klebanov, Polyakov, Witten

96 AdS/CFT correspondence 3+1 dimensional AdS space A 2+1 dimensional system at its quantum critical point Maldacena, Gubser, Klebanov, Polyakov, Witten

97 AdS/CFT correspondence Move away from the quantum critical point to a system of matter at non-zero density: equivalent to adding an electrical charge to the black hole. 3+1 dimensional AdS space Extremal Reissner- Nordtrom black hole Finite density matter in 2+1 dimensions

98 AdS/CFT correspondence Examine the free energy and Green s function of a probe particle T. Faulkner, H. Liu, J. McGreevy, and D. Vegh, arxiv: F. Denef, S. Hartnoll, and S. Sachdev, arxiv: dimensional AdS space Extremal Reissner- Nordtrom black hole Finite density matter in 2+1 dimensions

99 Green s function of a fermion T. Faulkner, H. Liu, J. McGreevy, and D. Vegh, arxiv: G(k, ω) 1 ω v F (k k F ) iω θ(k) See also S.-S. Lee, Phys. Rev. D 79, (2009); M. Cubrovic, J. Zaanen, and K. Schalm, Science 325, 439 (2009); F. Denef, S. A. Hartnoll, and S. Sachdev, Phys. Rev. D 80, (2009)

100 Green s function of a fermion T. Faulkner, H. Liu, J. McGreevy, and D. Vegh, arxiv: G(k, ω) 1 ω v F (k k F ) iω θ(k) See also S.-S. Lee, Phys. Rev. D 79, (2009); M. Cubrovic, J. Zaanen, and K. Schalm, Science 325, 439 (2009); F. Denef, S. A. Hartnoll, and S. Sachdev, Phys. Rev. D 80, (2009)

101 Green s function of a fermion A Fermi surface: Green s function is singular on a spherical surface at a non-zero k=kf. But the nature of the singularity differs from that in Landau s Fermi liquid theory. T. Faulkner, H. Liu, J. McGreevy, and D. Vegh, arxiv: G(k, ω) 1 ω v F (k k F ) iω θ(k) See also S.-S. Lee, Phys. Rev. D 79, (2009); M. Cubrovic, J. Zaanen, and K. Schalm, Science 325, 439 (2009); F. Denef, S. A. Hartnoll, and S. Sachdev, Phys. Rev. D 80, (2009)

102 Green s function of a fermion Non-Fermi liquid strange metal behavior in many spectral functions and transport properties qualitatively similar to observations in cuprate superconductors T. Faulkner, H. Liu, J. McGreevy, and D. Vegh, arxiv: G(k, ω) 1 ω v F (k k F ) iω θ(k) See also S.-S. Lee, Phys. Rev. D 79, (2009); M. Cubrovic, J. Zaanen, and K. Schalm, Science 325, 439 (2009); F. Denef, S. A. Hartnoll, and S. Sachdev, Phys. Rev. D 80, (2009)

103 Questions Can quantum fluctuations near the loss of antiferromagnetism induce higher temperature superconductivity? If so, why is there no antiferromagnetism in the hole-doped cuprates near the point where the superconductivity is strongest? What is the physics of the strange metal?

104 Questions and answers Can quantum fluctuations near the loss of antiferromagnetism induce higher temperature superconductivity? Yes If so, why is there no antiferromagnetism in the hole-doped cuprates near the point where the superconductivity is strongest? What is the physics of the strange metal?

105 Questions and answers Can quantum fluctuations near the loss of antiferromagnetism induce higher temperature superconductivity? Yes If so, why is there no antiferromagnetism in the hole-doped cuprates near the point where the superconductivity is strongest? Competition between antiferromagnetism and superconductivity has shifted the antiferromagnetic quantumcritical point (QCP), and shrunk the region of antiferromagnetism. This QCP shift is largest in the cuprates What is the physics of the strange metal?

106 Questions and answers Can quantum fluctuations near the loss of antiferromagnetism induce higher temperature superconductivity? Yes If so, why is there no antiferromagnetism in the hole-doped cuprates near the point where the superconductivity is strongest? Competition between antiferromagnetism and superconductivity has shifted the antiferromagnetic quantumcritical point (QCP), and shrunk the region of antiferromagnetism. This QCP shift is largest in the cuprates What is the physics of the strange metal? Proposal: strongly-coupled quantum criticality of Fermi surface change in a metal